Hydrogen supply system

ABSTRACT

A hydrogen supply system includes at least a hydrogen supply device for supplying hydrogen to a hydrogen storing device, and a hydrogen generating device producing hydrogen containing gas to be supplied to the hydrogen supply device. The hydrogen generating device produces the hydrogen containing gas by decomposing a fuel containing an organic compound, and includes a partition membrane, a fuel electrode provided on one surface of the partition membrane for generating hydrogen containing gas, a device for supplying a fuel containing the organic compound and water to the fuel electrode, an oxidizing electrode provided on the other surface of the partition membrane, a device for supplying an oxidizing agent to the oxidizing electrode, and a device for collecting the hydrogen containing gas directly from the fuel electrode.

TECHNICAL FIELD

The present invention relates to a hydrogen supply system for supplyinghydrogen to a hydrogen storing tank for supplying hydrogen to hydrogenstoring means such as a hydrogen storage container loaded on a fuel cellautomobile, a fuel cell automobile and the like.

Recently, as measures for problems of environment and natural resources,development of an electric automobile is actively pursued. As a fuelcell automobile, a fuel cell automobile loading a container storinghydrogen in the form of a hydrogen gas or a hydrogen storage alloy isbeing developed, but an important problem in its spread is improvementof hydrogen supply infrastructure. That is, how to improve the wide-areahydrogen supply infrastructure for freely running fuel cell automobilesis the problem. Then, a system in which a utility gas or a liquid fuel(desulfurized naphtha, gasoline, lamp oil, diesel oil, methanol, etc.)is steam-reformed by a reforming device at a hydrogen supply station andis stored in a hydrogen storage tank, and the hydrogen is supplied to ahydrogen storage container loaded on a fuel cell automobile is the mostactively developed since it has a merit that an existing infrastructuresuch as a utility gas piping network, a gas station and the like can beutilized at the maximum (See Patent Documents 1 to 4, for example).

However, the above hydrogen supply system has problems that thereforming device is expensive, the device size is large or maintenanceand operation thereof is complicated and requires an advancedtechnology.

[Patent Document 1] Japanese Unexamined Patent Application PublicationNo. 2002-315111

[Patent Document 2] Japanese Unexamined Patent Application PublicationNo. 2002-337999

[Patent Document 3] Japanese Unexamined Patent Application PublicationNo. 2003-118548

[Patent Document 4] Japanese Unexamined Patent Application PublicationNo. 2004-79262

Also, as the reforming device, development of a reforming device ofmethanol with the lowest reforming temperature is advanced, and threemethods of steam reforming, partial oxidization reforming and reformingusing both are employed (See Non-Patent Document 1), but in anyreforming method, in order to produce a hydrogen containing gas,reforming should be carried out at a temperature as high as 200° C. ormore, and there are problems of poisoning of reforming catalyst, removalof CO contained in the reformed gas (gas including hydrogen), mixture ofnitrogen in the air into the reformed gas obtained by partialoxidization reform or reform using the both methods.

[Non-patent Document 1] “Development and Practical Application of SolidPolymer type Fuel Cell”, PP 141 to 166, May 28, 1999, issued byTechnical Information Institute, Co., Ltd.

On the other hand, such a system in which water is electricallydecomposed to generate hydrogen instead of reforming a fuel containingan organic compound as above, this is stored in a hydrogen storage tankand this hydrogen is supplied to a hydrogen storage container loaded ona fuel cell automobile is under development (See Patent Documents 5 and6, for example).

According to this system, though a high temperature to reform a fuelcontaining an organic compound is not needed, there is a problem that alarge volume of electric power is required.

[Patent Document 5] Japanese Unexamined Patent Application PublicationNo. 2002-161998

[Patent Document 6] Japanese Unexamined Patent Application PublicationNo. 2002-363779

Moreover, an invention of a method for generating hydrogen byelectrochemical reaction (See Patent Documents 7, 9) and an invention ofa fuel cell using hydrogen generated by an electrochemical method (SeePatent Documents 8 to 10) are also known.

[Patent Document 7] Japanese Patent Publication No. 3328993

[Patent Document 8] Japanese Patent Publication No. 3360349

[Patent Document 9] U.S. Pat. Nos. 6,299,744, 6,368,492, 6,432,284,6,533,919, and United States Patent Publication No. 2003/0226763

[Patent Document 10] Japanese Unexamined Patent Application PublicationNo 2001-297779

Patent Document 7 cited above describes (claim 1), “a method forgenerating hydrogen comprising providing a pair of electrodes on the twoopposite surfaces of a cation exchange membrane, contacting a fuelcontaining at least methanol and water with one electrode having acatalyst, applying a voltage between the pair of electrodes so thatelectrons are withdrawn from the electrodes thereby causing a reactionto occur on the electrodes whereby hydrogen ions are generated frommethanol and water, and allowing hydrogen ions to be converted on theother electrode, being supplied with electrons, into hydrogenmolecules.” The same patent document discloses another method(paragraphs [0033] to [0038]) for selectively generating hydrogen usinga conversion system, the method comprising supplying water or watervapor together with methanol which serves as a fuel, providing a voltagevia an external circuit to cause electrons to be withdrawn from a fuelelectrode, so that reaction represented by CH₃OH+2H₂O→CO₂+6e⁻+6H⁺ occurson the fuel electrode, and allowing hydrogen ions thus produced to passthrough a cation exchange membrane to reach the opposite electrode wherethe hydrogen ions undergo reaction represented by 6H⁺+6e⁻→3H₂. PatentDocument 8 cited above describes (paragraphs [0052] to [0056]) a fuelcell which utilizes hydrogen generated by a method as described above.

According to the inventions described in Patent document 7 (paragraph[0042]) and Patent Document 8 (paragraph [0080]) cited above, it ispossible to generate hydrogen at a low temperature. However, the methodsdescribed in those inventions are obviously different from the hydrogengenerating device used in the hydrogen supply system of the presentinvention which will be given below in following points: those methodsrequire the application of voltage, and hydrogen is generated on theelectrode opposite to the electrode (fuel electrode) to which fuel issupplied, and no oxidizing agent is supplied to the opposite electrode.

This holds true also for the inventions disclosed by Patent Document 9cited above similarly to Patent Documents 7 and 8 cited above. Thoseinventions use a system for generating hydrogen where protons generatedon anode 112 serving as fuel electrode pass through partition membrane110 to reach cathode 114 opposite to the anode, and according to thesystem, voltage from DC power source 120 is applied between anode (fuelelectrode) and cathode (opposite electrode) to decompose organic fuelsuch as methanol or the like electrochemically. In addition, hydrogen isgenerated on the electrode opposite to the fuel electrode, and nooxidizing agent is supplied to the opposite electrode.

Patent Document 10 cited above discloses a fuel cell systemincorporating a hydrogen generating device. According to the disclosure(claim 1) of the invention, “Liquid fuel containing alcohol and water issupplied to porous electrode 1 (fuel electrode), air is supplied to gasdiffusion electrode 2 (oxidizing agent-applied electrode) opposite toelectrode 1, and a load is inserted between a terminal leading to porouselectrode 1 and another terminal leading to gas diffusion electrode 2 toachieve electric connection allowing a positive voltage to be applied toporous electrode 1 via the load from gas diffusion electrode 2 whichcorresponds to the positive electrode of MEA2 capable of acting as aconventional fuel cell.” The same patent document further adds(paragraph [0007]), “As a result, alcohol reacts with water to producecarbon dioxide gas and hydrogen ion, the hydrogen ion passes through anelectrolyte membrane 5 to reach a gas diffusion electrode 6 locatedcentrally where the hydrogen ion is converted into hydrogen gas. On theopposite surface of gas diffusion electrode 6 in contact with anotherelectrolyte layer 7, there arises another electrode reaction wherehydrogen gas is reconverted into hydrogen ion, and hydrogen ions migratethrough electrolyte layer 7 to reach another gas diffusion electrode 2where hydrogen ions react with oxygen in air to produce water.” Thus,with this system, electric energy generated by a fuel cell is utilizedto generate hydrogen on the hydrogen generating electrode (gas diffusionelectrode 6) which is then supplied to the fuel cell. Moreover, thesystem is the same with those described in the patent documents 7 to 9in that hydrogen is generated on the electrode opposite to the fuelelectrode.

There are some other known methods for generating hydrogen (See PatentDocuments 11 and 12). According to the inventions, a reaction systemwith a partition membrane is used where anode (electrode A) and cathode(electrode B) are placed opposite to each other with a proton conductingmembrane (ion conductor) inserted therebetween, and where alcohol(methanol) is oxidized with or without concomitant application ofvoltage, or with concomitant uptake of electric energy. All thosemethods, however, are based on a method whereby alcohol is oxidized bymeans of an electrochemical cell (the reaction product includes carbonicdiester, formalin, methyl formate, dimethoxymethane, etc.), and not on amethod whereby alcohol is converted by reduction into hydrogen.”

[Patent Document 11] Japanese Unexamined Patent Application PublicationsNo. 6-73582 (claims 1 to 3, paragraph [0050])

[Patent Document 12] Japanese Unexamined Patent Application PublicationsNo. 6-73583 (claims 1 and 8, paragraphs [0006] and [0019])

DISCLOSURE OF THE INVENTION

With a view to give a solution to the above problems, the presentinvention aims to provide a hydrogen supply system using a hydrogengenerating device which can easily supply hydrogen to a hydrogen storagetank for supplying hydrogen to hydrogen storing means such as a hydrogenstorage container loaded on a fuel cell automobile, a fuel cellautomobile, etc., for example and can produce a hydrogen containing gasat a low temperature and moreover, a large electric energy is notneeded.

Proposed to give a solution to the problems, the present invention canbe reduced to following constitutive elements.

(1) A hydrogen supply system provided with at least hydrogen supplymeans for supplying hydrogen to hydrogen storing means and a hydrogengenerating device producing hydrogen containing gas to be supplied tothe hydrogen supply means, wherein the hydrogen generating deviceproduces the hydrogen containing gas by decomposing a fuel containing anorganic compound and comprises a partition membrane, a fuel electrodeprovided on one surface of the partition membrane, means for supplying afuel containing the organic compound and water to the fuel electrode, anoxidizing electrode provided on the other surface of the partitionmembrane, means for supplying an oxidizing agent to the oxidizingelectrode, and means for collecting the hydrogen containing gas from thefuel electrode.

(2) The hydrogen supply system according to the above (1), wherein thehydrogen storing means is a hydrogen storage container loaded on a fuelcell automobile.

(3) The hydrogen supply system according to the above (1), wherein thehydrogen generating device is an open circuit having neither means forwithdrawing electric energy to outside from a hydrogen generating cellconstituting the hydrogen generating device, nor means for providingelectric energy from outside to the hydrogen generating cell.

(4) The hydrogen supply system according to the above (1) or (2),wherein the hydrogen generating device has means for withdrawingelectric energy to outside with the fuel electrode serving as a negativeelectrode and the oxidizing electrode as a positive electrode.

(5) The hydrogen supply system according to the above (1) or (2),wherein the hydrogen generating device has means for providing electricenergy from outside with the fuel electrode serving as cathode and theoxidizing electrode as anode.

(6) The hydrogen supply system according to the above (1) or (2),wherein two or more of hydrogen generating devices selected from a groupconsisting of a hydrogen generating device, which is an open circuithaving neither means for withdrawing electric energy to outside from ahydrogen generating cell, nor means for providing electric energy fromoutside to the hydrogen generating cell, a hydrogen generating devicehaving means for withdrawing electric energy to outside with the fuelelectrode serving as a negative electrode and the oxidizing electrode asa positive electrode, and a hydrogen generating device having means forproviding electric energy from outside with the fuel electrode servingas cathode and the oxidizing electrode as anode are combined in use.

(7) The hydrogen supply system according to the above (1) or (2),wherein voltage between the fuel electrode and the oxidizing electrodeis 200 to 1000 mV in the hydrogen generating device.

(8) The hydrogen supply system according to the above (3), whereinvoltage between the fuel electrode and the oxidizing electrode is 300 to800 mV in the hydrogen generating device.

(9) The hydrogen supply system according to the above (4), whereinvoltage between the fuel electrode and the oxidizing electrode is 200 to600 mV in the hydrogen generating device.

(10) The hydrogen supply system according to the above (4) or (9),wherein voltage between the fuel electrode and the oxidizing electrodeand/or the evolution volume of hydrogen-containing gas are/is adjustedby varying the volume of electric energy withdrawn from the hydrogengenerating device.

(11) The hydrogen supply system according to the above (5), whereinvoltage between the fuel electrode and the oxidizing electrode is 300 to1000 mV in the hydrogen generating device.

(12) The hydrogen supply system according to the above (5) or (11),wherein voltage between the fuel electrode and the oxidizing electrodeand/or the evolution volume of hydrogen-containing gas are/is adjustedby varying the volume of electric energy provided in the hydrogengenerating device.

(13) The hydrogen supply system according to any of the above (1) to(12), wherein the evolution volume of hydrogen-containing gas isadjusted by varying voltage between the fuel electrode and the oxidizingelectrode in the hydrogen generating device.

(14) The hydrogen supply system according to any of the above (1) to(13), wherein voltage between the fuel electrode and the oxidizingelectrode and/or the evolution volume of hydrogen-containing gas are/isadjusted by varying the supply volume of the oxidizing agent in thehydrogen generating device.

(15) The hydrogen supply system according to any of the above (1) to(14), wherein voltage between the fuel electrode and the oxidizingelectrode and/or the evolution volume of hydrogen-containing gas are/isadjusted by varying the concentration of the oxidizing agent in thehydrogen generating device.

(16) The hydrogen supply system according to any of the above (1) to(15), wherein voltage between the fuel electrode and the oxidizingelectrode and/or the evolution volume of hydrogen-containing gas are/isadjusted by varying the supply volume of fuel containing an organiccompound and water in the hydrogen generating device.

(17) The hydrogen supply system according to any of the above (1) to(16), wherein voltage between the fuel electrode and the oxidizingelectrode and/or the evolution volume of hydrogen-containing gas are/isadjusted by varying the concentration of fuel containing an organiccompound and water in the hydrogen generating device.

(18) The hydrogen supply system according to any of the above (1) to(17), wherein the operation temperature of the hydrogen generatingdevice is not higher than 100° C.

(19) The hydrogen supply system according to the above (18), wherein theoperation temperature is between 30 and 90° C.

(20) The hydrogen supply system according to any of the above (1) to(19), wherein the organic compound supplied to the fuel electrode of thehydrogen generating device is one or two or more organic compoundsselected from a group consisting of alcohol, aldehyde, carboxyl acid andether.

(21) The hydrogen supply system according to the above (20), wherein thealcohol is methanol.

(22) The hydrogen supply system according to any of the above (1) to(21), wherein the oxidizing agent supplied to the oxidizing electrode ofthe hydrogen generating device is an oxygen-containing gas or oxygen.

(23) The hydrogen supply system according to the above (22), wherein theoxidizing agent supplied to the oxidizing electrode of the hydrogengenerating device is an exhaust air exhausted from the hydrogengenerating device.

(24) The hydrogen supply system according to any of the above (1) to(21), wherein the oxidizing agent supplied to the oxidizing electrode ofthe hydrogen generating device is a liquid containing hydrogen peroxidesolution.

(25) The hydrogen supply system according to any of the above (1) to(24), wherein the partition membrane of the hydrogen generating deviceis a proton conducting solid electrolyte membrane.

(26) The hydrogen supply system according to the above (25), wherein theproton conducting solid electrolyte membrane is a perfluorocarbonsulfonate-based solid electrolyte membrane.

(27) The hydrogen supply system according to any of the above (1) to(26), wherein a catalyst of the fuel electrode of the hydrogengenerating device is made of platinum-ruthenium alloy supported bycarbon powder serving as a base.

(28) The hydrogen supply system according to any of the above (1) to(27), wherein a catalyst of the oxidizing electrode of the hydrogengenerating device is made of platinum supported by carbon powder servingas a base.

(29) The hydrogen supply system according to any of the above (1) to(28), wherein means for circulating fuel containing an organic compoundand water is provided at the hydrogen generating device.

(30) The hydrogen supply system according to any of the above (1) to(29), wherein a carbon dioxide absorbing portion for absorbing carbondioxide contained in the generated hydrogen-containing gas is providedat the hydrogen generating device.

(31) The hydrogen supply system according to any of the above (1) to(30), wherein a hydrogen permeable film is provided at the outlet of thehydrogen-containing gas of the hydrogen generating device.

(32) The hydrogen supply system according to any of the above (1) to(31), wherein an insulating material for insulating a heat generated bythe hydrogen generating device is not provided.

Here, the hydrogen generating device used in the hydrogen supply systemin the above (3) to (5) has the means for supplying the fuel and theoxidizing agent to the hydrogen generating cell constituting thehydrogen generating device, and as this means, a pump, a blower or thelike can be used. Besides that, in the case of the above (4), thedischarge control means for withdrawing electric energy from thehydrogen generating cell is provided, and in the case of the above (5),the electrolytic means for providing the electric energy to the hydrogengenerating cell is provided. The case of the above (3) is an opencircuit having neither discharge control means for withdrawing electricenergy from the hydrogen generating cell, nor electrolyte means forproviding electric energy from outside to the hydrogen generating cell.And the hydrogen generating device used in the hydrogen supply system inthe above (1) or (2) includes the hydrogen generating device used in thehydrogen supply system in the above (3) to (5). Moreover, these hydrogengenerating device have a function to control the supply volume orconcentration of the fuel and the oxidizing agent and the electricenergy to be withdrawn (in the case of the above (4)) or the electricenergy to be provided (in the case of the above (5)) by monitoring thevoltage of the hydrogen generating cell and/or the evolution volume ofhydrogen-containing gas. The basic construction of the hydrogengenerating cell constituting the hydrogen generating device is that thefuel electrode is provided on one surface of the partition membrane, astructure for supplying the fuel to the fuel electrode, while theoxidizing electrode is provided on the other surface of the partitionmembrane, a structure for supplying the oxidizing agent to the oxidizingelectrode.

Also, the fuel cell automobile is not limited to those obtaining adriving force of the vehicle only by a fuel cell but includes a hybridcar also using another power source.

EFFECT OF THE INVENTION

Since the hydrogen supply system of the present invention uses thehydrogen generating device which can reform the fuel at 100° C. or lessfrom a room temperature, which is extremely lower than the conventionalreforming temperature, both time required for start and energy amount toraise the temperature of a reformer can be reduced. Also, such effectsare exerted that an insulating material for insulating a heat generatedby the reforming device can be made unnecessary, and hydrogen can besupplied easily to a hydrogen storage tank for supplying hydrogen tohydrogen storing means such as a hydrogen storage container loaded on afuel cell automobile, a fuel cell automobile or the like, for example.

Moreover, since the hydrogen-containing gas generated from the hydrogengenerating device does not contain CO, a CO removing device is notneeded.

The hydrogen generating device used in the hydrogen supply system of thepresent invention can generate hydrogen without supplying the electricenergy from the outside to the hydrogen generating cell, but even if themeans for withdrawing the electric energy is provided, or the means forproviding the electric energy from the outside is provided, hydrogen canbe generated.

If the means for withdrawing the electric energy is provided, theelectric energy can be used for operating the pump, blower or otherauxiliary machines, and its effect is great in terms of effectiveutilization of energy.

Even if the means for providing the electric energy from the outside isprovided, by supplying a small amount of electric energy from theoutside to the hydrogen generating cell, hydrogen larger than theinputted electric energy can be generated, which is another effect.

Moreover, in any case, a process control is made possible by monitoringthe voltage of the hydrogen generating cell and/or the evolution volumeof the hydrogen-containing gas, the size of the hydrogen generatingdevice can be reduced, which can also reduce the manufacturing costs ofthe hydrogen supply system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a diagram for showing an example of a system flow of ahydrogen supply system of the invention.

FIG. 1( b) is a schematic diagram for showing an example of a hydrogengenerating device used in the hydrogen supply system of the invention.

FIG. 2 is a schematic diagram of a hydrogen generating cell (requiringno supply of electric energy from outside) described in Example 1.

FIG. 3 shows a graph for indicating relationship between the flow rateof air and the rate of hydrogen evolution when temperature is varied (30to 70° C.) (hydrogen generating example 1-1).

FIG. 4 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution when temperatureis varied (30 to 70° C.) (hydrogen generating example 1-1).

FIG. 5 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of air when theflow rate of fuel is varied (temperature being kept at 70° C.) (hydrogengenerating example 1-2).

FIG. 6 shows a graph for indicating relation of the rate of hydrogenevolution with the open-circuit voltage when the flow rate of fuel isvaried (temperature being kept at 70° C.) (hydrogen generating example1-2).

FIG. 7 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of air when theconcentration of fuel is varied (temperature being kept at 70° C.)(hydrogen generating example 1-3).

FIG. 8 shows a graph for indicating relation of the rate of hydrogenevolution with the open-circuit voltage when the concentration of fuelis varied (temperature being kept at 70° C.) (hydrogen generatingexample 1-3).

FIG. 9 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of air when thethickness of electrolyte membrane is varied (hydrogen generating example1-4).

FIG. 10 shows a graph for indicating relation of the rate of hydrogenevolution with the open-circuit voltage when the thickness ofelectrolyte membrane is varied (hydrogen generating example 1-4).

FIG. 11 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of air when thetemperature is varied (30 to 90° C.) (hydrogen generating example 1-5).

FIG. 12 shows a graph for indicating relation of the rate of hydrogenevolution with the open-circuit voltage when the temperature is varied(30 to 90° C.) (hydrogen generating example 1-5).

FIG. 13 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of air when theflow rate of fuel is varied (temperature: 50° C.) (hydrogen generatingexample 1-6).

FIG. 14 shows a graph for indicating relation of the rate of hydrogenevolution with the open-circuit voltage when the flow rate of fuel isvaried (temperature: 50° C.) (hydrogen generating example 1-6).

FIG. 15 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of air when theconcentration of fuel is varied (temperature: 50° C.) (hydrogengenerating example 1-7).

FIG. 16 shows a graph for indicating relation of the rate of hydrogenevolution with the open-circuit voltage when the concentration of fuelis varied (temperature: 50° C.) (hydrogen generating example 1-7).

FIG. 17 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of oxidizing gaswhen the concentration of oxygen is varied (temperature: 50° C.)(hydrogen generating example 1-8).

FIG. 18 shows a graph for indicating relation of the rate of hydrogenevolution with the open-circuit voltage when the concentration of oxygenis varied (temperature: 50° C.) (hydrogen generating example 1-8).

FIG. 19 shows a graph for indicating relations of the rate of hydrogenevolution and open-circuit voltage with the flow rate of H₂O₂ when thetemperature is varied (30 to 90° C.) (hydrogen generating example 1-10).

FIG. 20 shows a graph for indicating relation of the rate of hydrogenevolution (oxidizing agent: H₂O₂) with the open-circuit voltage when thetemperature is varied (30 to 90° C.)(hydrogen generating example 1-10).

FIG. 21 is a schematic diagram of a hydrogen generating cell (with meansfor withdrawing electric energy) described in Example 2.

FIG. 22 shows a graph for indicating relation of the operation voltage(discharging: temperature at 50° C.) with the current density withdrawnwhen the flow rate of air is varied (hydrogen generating example 2-1).

FIG. 23 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: temperature at 50° C.) with the operationvoltage when the flow rate of air is varied (hydrogen generating example2-1).

FIG. 24 shows a graph for indicating relation of the operation voltage(discharging: temperature at 30° C.) with the current density withdrawnwhen the flow rate of air is varied (hydrogen generating example 2-2).

FIG. 25 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: temperature at 30° C.) with the operationvoltage when the flow rate of air is varied (hydrogen generating example2-2).

FIG. 26 shows a graph for indicating relation of the operation voltage(discharging: temperature at 70° C.) with the current density withdrawnwhen the flow rate of air is varied (hydrogen generating example 2-3).

FIG. 27 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: temperature at 70° C.) with the operationvoltage when the flow rate of air is varied (hydrogen generating example2-3).

FIG. 28 shows a graph for indicating relation of the operation voltage(discharging: temperature at 90° C.) with the current density withdrawnwhen the flow rate of air is varied (hydrogen generating example 2-4).

FIG. 29 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: temperature at 90° C.) with the operationvoltage when the flow rate of air is varied (hydrogen generating example2-4).

FIG. 30 shows a graph for indicating relation of the operation voltage(discharging: flow rate of air at 50 ml/min) with the current densitywithdrawn when the temperature is varied.

FIG. 31 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: flow rate of air at 50 ml/min) with theoperation voltage when the temperature is varied.

FIG. 32 shows a graph for indicating relation of the operation voltage(discharging: flow rate of air at 100 ml/min) with the current densitywithdrawn when the temperature is varied.

FIG. 33 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: flow rate of air at 100 ml/min) with theoperation voltage when the temperature is varied.

FIG. 34 shows a graph for indicating relation of the operation voltage(discharging: temperature at 50° C.) with the current density withdrawnwhen the flow rate of fuel is varied (hydrogen generating example 2-5).

FIG. 35 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: temperature at 50° C.) with the operationvoltage when the flow rate of fuel is varied (hydrogen generatingexample 2-5).

FIG. 36 shows a graph for indicating relation of the operation voltage(discharging: temperature at 50° C.) with the current density withdrawnwhen the concentration of fuel is varied (hydrogen generating example2-6).

FIG. 37 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: temperature at 50° C.) with the operationvoltage when the concentration of fuel is varied (hydrogen generatingexample 2-6).

FIG. 38 shows a graph for indicating relation of the operation voltage(discharging: temperature at 50° C.) with the current density withdrawnwhen the concentration of oxygen is varied (hydrogen generating example2-7).

FIG. 39 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: temperature at 50° C.) with the operationvoltage when the concentration of oxygen is varied (hydrogen generatingexample 2-7).

FIG. 40 shows a graph for indicating relation of the operation voltage(discharging: oxidizing agent of H₂O₂) with the current densitywithdrawn when the temperature is varied (hydrogen generating example2-8).

FIG. 41 shows a graph for indicating relation of the rate of hydrogenevolution (discharging: oxidizing agent of H₂O₂) with the operationvoltage when the temperature is varied (hydrogen generating example2-8).

FIG. 42 is a schematic diagram of a hydrogen generating cell (with meansfor providing external electric energy) described in Example 3.

FIG. 43 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the current densityapplied when the flow rate of air is varied (hydrogen generating example3-1).

FIG. 44 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the operation voltagewhen the flow rate of air is varied (hydrogen generating example 3-1).

FIG. 45 shows a graph for indicating relation of the operation voltage(charging: temperature at 50° C.) with the current density applied whenthe flow rate of air is varied (hydrogen generating example 3-1).

FIG. 46 shows a graph for indicating relation of the energy efficiency(charging: temperature at 50° C.) with the operation voltage when theflow rate of air is varied (hydrogen generating example 3-1).

FIG. 47 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 30° C.) with the current densityapplied when the flow rate of air is varied (hydrogen generating example3-2).

FIG. 48 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 30° C.) with the operation voltagewhen the flow rate of air is varied (hydrogen generating example 3-2).

FIG. 49 shows a graph for indicating relation of the energy efficiency(charging: temperature at 30° C.) with the operation voltage when theflow rate of air is varied (hydrogen generating example 3-2).

FIG. 50 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 70° C.) with the current densityapplied when the flow rate of air is varied (hydrogen generating example3-3).

FIG. 51 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 70° C.) with the operation voltagewhen the flow rate of air is varied (hydrogen generating example 3-3).

FIG. 52 shows a graph for indicating relation of the energy efficiency(charging: temperature at 70° C.) with the operation voltage when theflow rate of air is varied (hydrogen generating example 3-3).

FIG. 53 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 90° C.) with the current densityapplied when the flow rate of air is varied (hydrogen generating example3-4).

FIG. 54 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 90° C.) with the operation voltagewhen the flow rate of air is varied (hydrogen generating example 3-4).

FIG. 55 shows a graph for indicating relation of the energy efficiency(charging: temperature at 90° C.) with the operation voltage when theflow rate of air is varied (hydrogen generating example 3-4).

FIG. 56 shows a graph for indicating relation of the rate of hydrogenevolution (charging: flow rate of air at 50 ml/min) with the currentdensity applied when the temperature is varied.

FIG. 57 shows a graph for indicating relation of the rate of hydrogenevolution (charging: flow rate of air at 50 ml/min) with the operationvoltage when the temperature is varied.

FIG. 58 shows a graph for indicating relation of the energy efficiency(charging: flow rate of air at 50 ml/min) with the operation voltagewhen the temperature is varied.

FIG. 59 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the current densityapplied when the flow rate of fuel is varied (hydrogen generatingexample 3-5).

FIG. 60 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the operation voltagewhen the flow rate of fuel is varied (hydrogen generating example 3-5).

FIG. 61 shows a graph for indicating relation of the energy efficiency(charging: temperature at 50° C.) with the operation voltage when theflow rate of fuel is varied (hydrogen generating example 3-5).

FIG. 62 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the current densityapplied when the concentration of fuel is varied (hydrogen generatingexample 3-6).

FIG. 63 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the operation voltagewhen the concentration of fuel is varied (hydrogen generating example3-6).

FIG. 64 shows a graph for indicating relation of the energy efficiency(charging: temperature at 50° C.) with the operation voltage when theconcentration of fuel is varied (hydrogen generating example 3-6).

FIG. 65 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the current densityapplied when the concentration of oxygen is varied (hydrogen generatingexample 3-7).

FIG. 66 shows a graph for indicating relation of the rate of hydrogenevolution (charging: temperature at 50° C.) with the operation voltagewhen the concentration of oxygen is varied (hydrogen generating example3-7).

FIG. 67 shows a graph for indicating relation of the energy efficiency(charging: temperature at 50° C.) with the operation voltage when theconcentration of oxygen is varied (hydrogen generating example 3-7).

FIG. 68 shows a graph for indicating relation of the rate of hydrogenevolution (charging: oxidizing agent of H₂O₂) with the current densityapplied when the temperature is varied (hydrogen generating example3-8).

FIG. 69 shows a graph for indicating relation of the rate of hydrogenevolution (charging: oxidizing agent of H₂O₂) with the operation voltagewhen the temperature is varied (hydrogen generating example 3-8).

FIG. 70 shows a graph for indicating relation of the energy efficiency(charging: oxidizing agent of H₂O₂) with the operation voltage when thetemperature is varied (hydrogen generating example 3-8).

FIG. 71 is a graph for indicating relation of the air flow rate and therate of hydrogen evolution (open circuit: temperature at 50° C.)(Example 8).

FIG. 72 is a graph for indicating relation of the open voltage and therate of hydrogen evolution (open circuit: temperature at 50° C.)(Example 8).

REFERENCE NUMERALS

10. Hydrogen generating cell

11. Partition membrane

12. Fuel electrode

13. Feed channel for supplying fuel containing organic compound andwater (aqueous solution of methanol)

14. Oxidizing electrode (air electrode)

15. Feed channel for supplying oxidizing agent (air)

16. Fuel pump

17. Air blower

18. Fuel flow control valve

19. Air flow control valve

20. Fuel tank

21. Fuel control vessel

22. Voltage controller

23. Gas/liquid separator

24. Guide tube

BEST MODE FOR CARRYING OUT THE INVENTION

The most preferred embodiments in the execution of the present inventionwill be illustrated below.

The hydrogen generating device used in the hydrogen supply system of theinvention is basically novel, and the embodiments thereof describedherein are given only for the illustrative representation of theinvention, and not for limiting the scope of the invention.

The basic construction of the hydrogen supply system of the inventioncomprises, if the hydrogen storing means is a hydrogen storage containerloaded on a fuel cell automobile, hydrogen supply means for supplyinghydrogen to the hydrogen storage container and a hydrogen generatingdevice for generating a hydrogen containing gas to be supplied to thehydrogen supply means.

FIG. 1( a) shows an example of a system flow of the hydrogen supplysystem of the invention.

The hydrogen supply means for supplying hydrogen to the hydrogen storagecontainer loaded on the fuel cell automobile comprises, for example, ahydrogen booster machine, a high-pressure hydrogen storage tank, and ahydrogen dispenser.

As the hydrogen booster machine, a hydrogen compression pump isgenerally used, but any device can be used only if the pressure ofhydrogen can be boosted. The hydrogen gas pressure at the hydrogenbooster outlet is preferably higher in view of a volume efficiency,preferably at 50 atmospheric pressure (5 MPa) or more, more preferablyat 100 atmospheric pressure (10 MPa) or more or further preferably at200 atmospheric pressure (20 MPa) or more. An upper limit is notparticularly limited, but 1000 atmospheric pressure (100 MPa) or less ispreferable.

After the hydrogen-pressure boosting process, a hydrogen storage tank(high-pressure hydrogen storage tank) is preferably provided for storinghydrogen. As the high-pressure hydrogen storage tank, its form is notparticularly limited only if it can withstand the boosted hydrogen, anda publicly known device can be used. Besides a high-pressure hydrogenstorage tank for storing a high-pressure hydrogen gas as it is, ahigh-pressure hydrogen storage tank incorporating a hydrogen storagealloy can be used.

The hydrogen gas is guided to the hydrogen dispenser from thehigh-pressure hydrogen storage tank. Alternatively, the outlet gas ofthe hydrogen booster can be directly guided to the hydrogen dispenserwithout going through the high-pressure hydrogen storage tank. In thatcase, a piping is provided for connecting the hydrogen boosting machineto the hydrogen dispenser.

The hydrogen dispenser is to supply a hydrogen gas to the hydrogenstorage container of the fuel cell automobile using hydrogen as a fuel,and a publicly known dispenser can be used. This hydrogen storagecontainer may be a hydrogen storage container as loaded on a fuel cellautomobile, and if this container can be removed from the fuel cellautomobile, it may be the hydrogen storage container in the stateremoved from the fuel cell automobile.

One example of the hydrogen generating device used in the hydrogensupply system of the invention is shown in FIG. 1( b). This hydrogengenerating device has a hydrogen generating cell (10) and auxiliarycomponents for driving the hydrogen generating device.

Since the hydrogen generating device operates at a low temperature, itis not necessary to provide a heater to raise the temperature as shownin FIG. 1( b), the heater may be provided as necessary.

Structurally, the hydrogen generating cell (10) comprises a fuelelectrode (12) provided on one surface of a partition membrane (11), afeed channel (13) through which fuel containing an organic compound andwater (aqueous solution of methanol) is supplied to the fuel electrode(12), an oxidizing electrode (14) provided on the other surface ofpartition membrane (11), and another feed channel (15) through which anoxidizing agent (air) is supplied to the oxidizing electrode (14).

Auxiliary components for supporting the operation of the hydrogengenerating system comprise a fuel pump (16) for supplying the aqueoussolution of methanol to fuel electrode (12) and an air blower forsupplying air to oxidizing electrode (14).

The feed channel (13) to fuel electrode is connected via a guide tubeoperation through a flow control valve (18) to fuel pump (16). The feedchannel (15) to oxidizing electrode is connected via a guide tubeoperation through a flow control valve (19) to air blower (17).

Fuel (100% methanol) is stored in a fuel tank (20). Fuel is transferredto a fuel control vessel (21) where fuel is mixed with water to give,for example, about 3% aqueous solution of methanol. The aqueous solutionis then supplied to fuel electrode (12).

Also, if two or more hydrogen generating devices are used incombination, as air to be supplied to the oxidizing electrode (14) ofone of the hydrogen generating cells (10), an exhaust air exhausted fromthe other hydrogen generating cell (10) can be used.

According to the hydrogen generating system configured as describedabove, when electric energy is supplied to fuel pump (16) and air blower(17) to drive them into action, and flow control valve (18) is opened,by virtue of the activated fuel pump (16), the aqueous solution ofmethanol is transported from fuel control vessel (21) through channel(13) to fuel electrode (12). On the other hand, when the flow controlvalve (19) is opened, by virtue of the activated air blower, air istransported through channel (15) to oxidizing electrode (14).

As a result of the aforementioned operation, reactions as describedbelow will occur on the fuel electrode and on the oxidizing (air)electrode which will result in the generating of hydrogen-containing gason the fuel electrode (12).

The evolution volume of hydrogen-containing gas is adjusted by providinga voltage controller (22) for monitoring the voltage (open-circuitvoltage or operation voltage) of hydrogen generating cell (10), and bycontrolling as appropriate the supply volume or concentration of fueland air, or the magnitude of electric energy withdrawn from or providedto the cell based on the monitor result.

Hydrogen-containing gas is allowed to pass through a gas/liquidseparator (23) so that hydrogen-containing gas is separated fromunreacted aqueous solution of methanol, and part or all of the unreactedaqueous solution of methanol may be returned to fuel control vessel (21)by means of a circulating means comprising a guide tube (24). In certaincases as needed, water may be supplied from outside to the solution.

The hydrogen generating cell (10) in the hydrogen generating device usedin the hydrogen supply system of the invention is basically composed ofa partition membrane (11), a fuel electrode (12) provided on one surfaceof partition membrane (11) and an oxidizing electrode (14) provided onthe other surface of partition membrane as described above. The elementconfigured as described above may be represented by an MEA(membrane/electrode assembly) used in a direct methanol fuel cell.

The method for fabricating an MEA is not limited to any specific one,but a method similar to a conventional one may be employed wherein afuel electrode and an oxidizing electrode (air electrode) with apartition membrane inserted therebetween are compressed at a hightemperature to be assembled.

Suitable partition membranes may include a proton conducting solidelectrolyte membrane which has been used as a polymer electrolytemembrane of a fuel cell. The proton conducting solid electrolytemembrane preferably includes a membrane based on perfluorocarbonsulfonate having sulfonic acid group such as Nafion provided by Dupont.

The fuel electrode or oxidizing (air) electrode is preferably anelectrode which is conductive and has a catalytic activity. Productionof such an electrode may be achieved by applying a catalyst paste onto agas diffusion layer and drying the paste, wherein the paste is comprisedof a catalyst with carbon powder serving as a base, a binding agent suchas a PTFE resin, and an ion conductivity conferring substance such asNafion solution.

The gas diffusion layer is preferably made of a carbon paper treated tobe water-repellent.

The catalyst to be applied to fuel electrode is not limited to anyspecific one, but is preferably a platinum-ruthenium alloy supported bycarbon powder serving as a base.

The catalyst applied to air electrode is not limited to any specificone, but is preferably platinum supported by carbon powder serving as abase.

For a hydrogen generating device configured as described above, whenfuel containing an organic compound such as an aqueous solution ofmethanol is supplied to the fuel electrode, and an oxidizing agent suchas air, oxygen or hydrogen peroxide is supplied to the oxidizing (air)electrode, gas containing hydrogen evolves on the fuel electrode underspecified conditions.

In the hydrogen generating device used in the hydrogen supply system ofthe invention, the hydrogen generating method are quite different fromconventional hydrogen generating methods, and it is still difficult atpresent to explain the mechanism. The hypothesis which is currentlythought most likely to be true will be described below, but it can notbe denied that the hypothesis would be upset by new reactions which willshed new light to the phenomenon.

According to the hydrogen generating device used in the hydrogen supplysystem of the invention, hydrogen-containing gas evolves, at atemperature as low as 30 to 90° C., from the fuel electrode whichreceives the supply of methanol and water as will be described below.When no electric energy is supplied from outside to the hydrogengenerating cell, gas containing hydrogen at 70 to 80% evolves, whilewhen electric energy is supplied from outside to the cell, gascontaining hydrogen at 80% or higher evolves. The evolution of gasdepends on the open circuit voltage or operation voltage between the twoelectrodes. Base on these results, the most likely explanation of themechanism underlying the evolution of hydrogen is as follows. Forbrevity, description will be given below on the premise that the cell iskept under circuit-open condition.

Let's assume for example that methanol is applied, as fuel, to ahydrogen generating device of the invention. Firstly proton is likely tobe generated on the fuel electrode by virtue of a catalyst, as is thecase with a DMFC.CH₃OH+H₂O→CO₂+6H⁺+6e ⁻  (1)

When Pt—Ru is used as a catalyst, methanol is adsorbed to the surface ofPt, and undergoes a series of electrochemical oxidization reactions asdescribed below, resulting in the production of chemical species firmlyadhered to the surface of the catalyst ultimately leading to reaction(1) described above, so it is contended (“Handbook of Electric Cell,”Feb. 20, 2001, p. 406, Maruzen, 3rd edition).CH₃OH+Pt→Pt—(CH₃OH)ads→Pt—(CH₂OH)ads+H⁺ +e ⁻Pt—(CH₂OH)ads→Pt—(CHOH)ads+H⁺ +e ⁻Pt—(CHOH)ads→Pt—(COH)ads+H⁺ +e ⁻Pt—(COH)ads→Pt—(CO)ads+H⁺ +e ⁻

To further oxidize Pt—(CO)ads, it is necessary to prepare (OH)ads fromwater.Ru+H₂O→Ru—(H₂O)ads→Ru—(OH)ads+H⁺ +e ⁻Ru—(OH)ads+Pt—(CO)ads→Ru+Pt+CO₂+H⁺ +e ⁻

For a DMFC, H⁺ (proton) generated on the fuel electrode as a result ofthe reaction represented by formula (1) migrates through a protonconducting solid electrolyte membrane to reach the oxidizing electrodewhere it reacts with oxygen-containing gas or oxygen supplied to theoxidizing electrode as represented by the following reaction formula.3/2O₂+6H⁺+6e ⁻→3H₂O  (2)

Since the hydrogen generating device works under open-circuit condition,e⁻ generated as a result of the reaction represented by formula (1) cannot be supplied through an external circuit to the oxidizing electrode.Therefore, for the reaction represented by formula (2) to occur, it isnecessary to supply e⁻ to the oxidizing electrode from a differentreaction.

By the way, with regard to a DMFC using a proton conducting solidelectrolyte membrane such as Nafion, there has been known a phenomenoncalled methanol crossover, that is, the crossover of methanol from thefuel electrode to the oxidizing electrode. Thus, it is possible thatcrossed methanol undergoes electrolytic oxidization represented by thefollowing formula on the oxidizing electrode.CH₃OH+H₂O→CO₂+6H⁺+6e ⁻  (3)

If the reaction represented by formula (3) occurs, e⁻ produced as aresult of the reaction is supplied to allow the reaction represented byformula (2) to occur there.

The H⁺ (proton) produced as a result of the reaction represented byformula (3) migrates through the proton conducting solid electrolytemembrane to reach the fuel electrode to undergo there a reactionrepresented by the following formula to produce hydrogen.6H⁺+6e ⁻→3H₂  (4)

In this sequence of reactions, the transfer of H⁺ and e⁻ produced as aresult of the reaction represented by formula (1) on the fuel electrodeto the oxidizing electrode and the transfer of H⁺ and e⁻ produced as aresult of the reaction represented by formula (3) on the oxidizingelectrode to the fuel electrode are likely to be apparently canceled outby each other.

Then, on the oxidizing electrode there arises reaction as represented byformula (2) based on H⁺ and e⁻ produced as a result of the reactionrepresented by formula (3), while on the fuel electrode there arisesreaction as represented by formula (4) based on H⁺ and e⁻ produced as aresult of the reaction represented by formula (1).

Assumed that reactions represented by formulas (1) and (4) occur on thefuel electrode while reactions represented by formulas (2) and (3) occuron the oxidizing electrode, the net balance of chemical reactions islikely to be expressed by the following formula (5).2CH₃OH+2H₂O+3/2O₂→2CO₂+3H₂O+3H₂  (5)

The theoretical efficiency of this reaction is 59% (calorific value of 3mol. hydrogen/calorific value of 2 mol. methanol).

The standard electrode potential E0 of the reaction represented byformula (1) is E0=0.046 V, while the standard electrode potential E0 ofthe reaction represented by formula (4) is E0=0.0 V. Thus, if the tworeactions are combined to form a cell, the electrode where the reactionof formula (1) will occur will serve as a positive electrode while theelectrode where the reaction of formula (4) will occur will serve as anegative electrode. The reaction of formula (1) will proceed in thedirection opposite to the arrow represented direction. Similarly, thereaction of formula (4) will also proceed in the direction opposite tothe arrow represented direction. Thus, the cell will not generatehydrogen.

For the cell to generate hydrogen, it is necessary to make both thereactions of formulas (1) and (4) proceed in the direction representedby the arrow. For this purpose, it is absolutely necessary to make thereaction of formula (1) occur on a negative electrode and the reactionof formula (4) on a positive electrode. If it is assumed that the entirearea of fuel electrode is uniformly at a constant level, it is necessaryto shift the methanol oxidizing potential to a lower level or to shiftthe hydrogen generating potential to a higher level.

However, if the entire area of fuel electrode is not at a constantpotential level, reaction on the fuel electrode where methanol and waterreact to produce H⁺ according to formula (1) and reaction on theoxidizing electrode where H⁺ and e⁻ react to produce hydrogen accordingto formula (4) are likely to proceed simultaneously.

As will be described later in relation to Example, a reaction systemexposed to a higher temperature is more apt to generate hydrogen, andthus endothermic reactions (1) and (3) are likely to proceed in thearrow-indicated direction, being supplied heat from outside via otherexothermic reactions.

Methanol not only undergoes reactions as represented by formulas (1) and(3), but is also subject, as a result of crossover, to the subsidiaryreaction where methanol permeating from the fuel electrode is oxidizedby oxygen on the surface of catalyst coated on the air electrode asrepresented by the following formula.CH₃OH+3/2O₂→CO₂+2H₂O  (6)

Since the reaction of formula (6) is an exothermic reaction, heatgenerated by this reaction is most likely to be used to allow reactionsrepresented by formulas (1) and (3) to occur.

With regard to a hydrogen generating device used in the hydrogen supplysystem as described in claim 3 of the invention (open-circuit conditionhereinafter), as apparent in relation to Example described later, supplyof oxygen (air) is decreased, and when the open-circuit voltage is 300to 800 mV, hydrogen evolves. However, this is probably because theoxidation of methanol permeated to air electrode as represented byformula (6) is suppressed, evolution reaction of H⁺ as represented byformula (3) becomes dominant, and the H⁺ undergoes reaction representedby formula (4) to produce hydrogen.

With regard to a hydrogen generating device used in the hydrogen supplysystem as described in claim 4 of the invention (discharging conditionhereinafter), hydrogen is likely to be generated depending on the samemechanism as in the open-circuit condition. However, in contrast withthe open-circuit condition, it is necessary with this system for H⁺corresponding in volume to discharge current to migrate from the fuelelectrode to the oxidizing electrode in order to establish theneutralized electrical condition of the cell. Therefore, it is likelythat reaction of formula (1) rather than reaction of formula (4) willoccur on the fuel electrode while reaction of formula (2) rather thanreaction of formula (3) will occur on the oxidizing electrode.

If discharge current becomes large (because of a large volume of e⁻being supplied to the oxidizing electrode), and if discharge voltage islower than 200 mV, hydrogen will not evolve as will be described laterin relation to Example. This is probably because the voltage is not sohigh as to permit the aqueous solution of methanol to be electrolyzed.

If a large volume of oxygen (air) is supplied or discharge voltage ishigher than 600 mV, hydrogen will not evolve either. This is probablybecause methanol permeated to the air electrode is oxidized thereaccording to the reaction shown in formula (6), instead of the H⁺evolution reaction shown in formula (3).

On the contrary, if supply of oxygen (air) is marginal, the dischargecurrent will be reduced, and if discharge voltage (operation voltage)becomes 200 to 600 mV, hydrogen will still evolve. However, this isprobably because the oxidation of methanol permeated to the airelectrode as represented by formula (6) is suppressed, evolutionreaction of H⁺ as represented by formula (3) becomes dominant, and theH⁺ undergoes reaction represented by formula (4) to produce hydrogen.

With regard to a hydrogen generating device used in the hydrogen supplysystem as described in claim 5 of the invention (charging conditionhereinafter), hydrogen is likely to be generated depending on the samemechanism as in the open-circuit condition. However, in contrast withthe open-circuit condition, it is necessary with this system for H⁺corresponding in volume to electrolysis current to migrate from theoxidizing electrode to the fuel electrode in order to establish theneutralized electrical condition of the cell. Therefore, it is likelythat reaction of formula (4) rather than reaction of formula (1) willoccur on the fuel electrode while reaction of formula (3) rather thanreaction of formula (2) will occur on the oxidizing electrode.

To put it more specifically, with regard to the charging condition wherethe fuel electrode serves as cathode while the oxidizing electrodeserves as anode, electric energy is supplied from outside (e⁻ issupplied from outside to the fuel electrode). Then, basicallyelectrolysis occurs in the system. As electric energy supplied (voltageapplied) is increased, more hydrogen will be produced. This is probablybecause as more e⁻ is supplied from outside to the fuel electrode,oxidization of methanol represented by formula (3) and reactionrepresented by formula (4) (6H⁺+6e⁻→3H₂) will be more enhanced as willbecome apparent from the description given below in relation to Example.

However, as will be described later, if supply of oxygen (air) ismarginal, the energy efficiency of the system becomes high when appliedvoltage (operation voltage) is at a low range of 400 to 600 mV. This isprobably because the oxidation of methanol permeated to air electrode asrepresented by formula (6) is suppressed, evolution reaction of H⁺ asrepresented by formula (3) becomes dominant, and the H⁺ undergoesreaction represented by formula (4) to produce hydrogen in the samemanner as described above even in the case of open-circuit condition ordischarging condition where electric energy is not provided fromoutside. Evolution of hydrogen in the charging condition is likely to begenerated depending on the same mechanism as in the open-circuitcondition and discharging condition as well as on the electric energysupplied from outside.

The meaning of the potential of the cell will be described here.Generally, the voltage of a cell having two electrodes with anelectrolyte membrane inserted therebetween is determined by thedifference between the two electrodes of chemical potentials of ionswhich serve as conductors in electrolyte.

If polarizations at the two electrodes are ignored, the voltage inquestion indicates the difference between the two electrodes of chemicalpotentials of hydrogen, in other words, partial pressures of hydrogen,since this cell uses a proton (hydrogen ion) conducting solidelectrolyte membrane.

According to the invention, as will be described later in relation toExample, if there is voltage between the fuel and oxidizing electrodesthat is in a certain range, this indicates the evolution of hydrogen onthe fuel electrode. Thus, if the difference of chemical potentials ofhydrogen between the two electrodes falls within a certain range,reactions as represented by formulas (1) to (6) cited above will proceedwhich will result in the production of hydrogen.

According to the hydrogen generating device used in the hydrogen supplysystem of the invention, it is possible to adjust the evolution volumeof hydrogen-containing gas by varying the voltage (open-circuit voltageor operation voltage) between the fuel electrode and oxidizing (air)electrode, regardless of whether electric energy is withdrawn to outsidefrom the hydrogen generating cell of the system or whether electricenergy is supplied from outside to the hydrogen generating cell.

As will be described below in relation of Example, the open-circuitcondition evolves hydrogen at the open-circuit voltage of 300 to 800 mV;the discharging condition evolves hydrogen at the discharge voltage(operation voltage) of 200 to 600 mV; and the charging condition evolveshydrogen at the applied voltage (operation voltage) of 300 to 1000 mV(energy efficiency is high at 400 to 600 mV). Thus, it is possible toadjust the evolution volume of hydrogen-containing gas by varyingopen-circuit voltage or operation voltage in accordance with the voltagerange cited above.

As will be described below in relation of Example, it is possible toadjust the open-circuit voltage or operation voltage and/or theevolution volume (rate of hydrogen evolution) of hydrogen-containing gasby varying the supply volume of an oxidizing agent (oxygen-containinggas or oxygen, or hydrogen peroxide-containing liquid), or theconcentration of an oxidizing agent (oxygen concentration ofoxygen-containing gas), or the supply volume of organiccompound-containing fuel, or the concentration of organiccompound-containing fuel.

It is also possible to adjust the operation voltage and/or the evolutionvolume of hydrogen-containing gas by varying, for the dischargingcondition, electric energy withdrawn to outside, (varying currentwithdrawn to outside, or varying the voltage withdrawn to outside usinga constant-voltage controllable power source, for example, so-calledpotentiostat), or, for the charging condition, electric energy suppliedto the system (or current supplied to the system, or by varying thevoltage of the system using a constant-voltage power source, forexample, so-called potentiostat).

Since according to the hydrogen generating device used in the hydrogensupply system of the invention, it is possible to decompose organiccompound-containing fuel at 100° C. or lower, the temperature at whichthe system can be operated is made 100° C. or lower. The operationtemperature is preferably 30 to 90° C. This is because, when theoperation temperature is adjusted to be between 30 and 90° C., it willbecome possible to adjust the open-circuit voltage or operation voltage,and/or the evolution volume of hydrogen-containing gas as will bedescribed later in relation to Example.

Incidentally, for a hydrogen generating cell based on conventional fuelconversion technology, the operation temperature should be kept at 100°C. or higher. At this temperature range, water will become vapor andorganic compound-containing fuel become gas, and even when hydrogenevolves under this condition, it is necessary to provide meansspecifically adapted for separating hydrogen. The system of the presentinvention is also advantageous in this point.

Indeed, there will arise a problem as described above, when organiccompound-containing fuel is decomposed at 100° C. or higher. But ahydrogen generating device used in the hydrogen supply system of theinvention may be operated at a temperature slightly above 100° C. ifthere be need to do so.

As long as based on the putative principle, the organiccompound-containing fuel may be liquid or gaseous fuel capable ofproducing proton as a result of electrochemical oxidization that canpass through a proton conductive partition membrane, and liquid fuelcontaining alcohol such as methanol, ethanol, ethylene glycol,2-propanol, aldehyde such as formaldehyde, carboxyl acid such as formicacid, or ether such as diethyl ether is preferred. Since the organiccompound-containing fuel is supplied with water, an aqueous solution ofalcohol, particularly aqueous solution of methanol is preferred. Theaqueous solution of methanol cited above as a preferred example of fuelis an aqueous solution containing at least methanol, and itsconcentration of methanol at a region where hydrogen-containing gasevolves may be arbitrarily determined as needed.

Suitable oxidizing agents may include gaseous or liquid oxidizingagents. Suitable gaseous oxidizing agents may include oxygen-containinggas or oxygen. The concentration of oxygen in oxygen-containing gas ispreferably chosen to be 10% or higher particularly. Suitable liquidoxidizing agents may include hydrogen peroxide-containing liquid.

For a hydrogen generating device of the invention, since the fraction offuel converted into hydrogen is rather small, it is desirable to providefuel circulating means to improve thereby the fraction of fuel to beconverted into hydrogen.

The hydrogen generating device used in the hydrogen supply system of theinvention has means for collecting hydrogen-containing gas provided fromthe fuel electrode. The means is preferably so constructed as to be ableto recover carbon dioxide as well as hydrogen. Since the system operatesat a temperature as low as 100° C. or lower, it is possible to attach acarbon dioxide absorbing portion for absorbing carbon dioxide containedin hydrogen-containing gas to the system by simple means.

Also, the hydrogen-containing gas generated from the fuel electrode ofthe hydrogen generating device contains not only carbon dioxide butwater, unreacted raw material, etc., and it is preferable to provide ahydrogen permeable film at the outlet of the hydrogen-containing gas ofthe hydrogen generating device to have selectively only hydrogenpermeate to have a hydrogen with high purity.

The hydrogen permeable film is not limited but a hydrogen permeablemetal film with the thickness of 5 to 50 μm and formed on an inorganicporous layer to have selectively hydrogen permeate may be used. Theinorganic porous layer is a carrier for holding the hydrogen permeablemetal film and is formed from a porous stainless-steel unwoven cloth,ceramics, glass and the like within the range of thickness form 0.1 mmto 1 mm. As the hydrogen permeable metal film, an alloy containing Pd,an alloy containing Ni or an alloy containing V can be used, but thealloy containing Pd is preferable. As the alloy containing Pd, there arePd/Ag alloy, Pd/Y alloy, Pd/Ag/Au alloy or the like.

By the above hydrogen permeable film, a high-purity hydrogen with thepurity of 99.999% or more can be obtained, and this high-purity hydrogenis useful as a fuel for a fuel cell or a treatment gas or the like whenproducing a semiconductor device.

If the hydrogen generated by the hydrogen generating device is to besupplied to a hydrogen cylinder used as the treatment gas for thesemiconductor or the like, it is preferably supplied to the hydrogencylinder through a compressor, a carbon dioxide absorbing portion and ahydrogen permeable film and from the hydrogen cylinder to the hydrogentreating device of the semiconductor or the like.

Next, illustrative examples (examples of hydrogen generating) of thepresent invention will be presented. However, the fractions ofcatalysts, PTFE, Nafion, etc., and the thickness of catalyst layer, gasdiffusion layer and electrolyte membrane are not limited to the valuescited in the examples, but may take any appropriate values.

EXAMPLE 1

Illustrative examples of generating hydrogen based on the hydrogengenerating device used in the hydrogen supply system (open-circuitcondition) as defined by claim 3 of the invention will be presentedbelow.

Hydrogen Generating Example 1-1

Hydrogen generating cells described in Example 1 (generating examples1-1 to 1-10) have the same structure as that of representative DMFCs.

The structure of the hydrogen generating cell is outlined in FIG. 2.

The electrolyte membrane consists of a proton conducting electrolytemembrane provided by Dupont (Nafion 115); and the air electrode isobtained by immersing carbon paper (Toray) in a solution wherepolytetrafluoroethylene is dispersed at 5%, and baking the paper at 360°C. to make it water-repellent, and coating, on one surface of the paper,air electrode catalyst paste comprised of air electrode catalyst(carbon-supported platinum, Tanaka Precious Metal), fine powder of PTFE,and 5% Nafion solution (Aldrich). Thus, the air electrode exists as agas diffusion layer with air electrode catalyst. In the preparation ofthe air electrode catalyst paste, the percent contents by weight of airelectrode catalyst, PTFE, and Nafion were made 65%, 15% and 20%,respectively. The loading level of catalyst of the air electrodeprepared as above was 1 mg/cm² in terms of the weight of platinum perunit area.

Another carbon paper was similarly treated to be made water-repellent.One surface of the paper was coated with fuel electrode catalyst pastecomprised of fuel electrode catalyst (carbon-supportedplatinum-ruthenium, Tanaka Precious Metal), fine powder of PTFE, and 5%Nafion solution. Thus, the fuel electrode exists as a gas diffusionlayer with fuel electrode catalyst. In the preparation of the fuelelectrode catalyst paste, the percent contents by weight of fuelelectrode catalyst, PTFE, and Nafion were made 55%, 15% and 30%,respectively. The loading level of catalyst of the fuel electrodeprepared as above was 1 mg/cm² in terms of the weight ofplatinum-ruthenium per unit area.

The electrolyte membrane, gas diffusion layer with air electrodecatalyst and gas diffusion layer with fuel electrode catalyst were laidone over another to be hot-pressed at 140° C. under a pressure of 100kg/cm² so that they were assembled to form an MEA. The MEA prepared asabove had an active electrode area of 60.8 cm². The thicknesses of airand fuel electrode catalyst layers were practically the same about 30μm, and the thicknesses of air and fuel electrode gas diffusion layerswere similarly the same about 170 μm.

The MEA was further provided on its both surfaces with flow passagesthrough which air can flow and fuel can flow, and was enclosed fromoutside with an air electrode separator and a fuel electrode separatorrespectively both made of graphite into which phenol resin isimpregnated, in order to prevent the leak of gas from the MEA. Tofurther ensure the seal of MEA against the leak of fuel and air, MEA wassurrounded with silicon-rubber made packing.

The hydrogen generating cell prepared as above was placed in an electricfurnace where hot air was circulated. The temperature (operationtemperature) of the cell was kept at 30 to 70° C., air was flowed at arate of 0 to 400 ml/min to the air electrode, and 0.5 to 2M aqueoussolution of methanol (fuel) was flowed at a rate of 2 to 15 ml/min tothe fuel electrode. Then, the voltage difference between the fuelelectrode and the air electrode (open voltage), the volume of gasevolved on the fuel electrode and the composition of the gas weremonitored and analyzed.

First, the flow rate of aqueous solution of methanol (fuel) to the cellwas kept 8 ml/min, and the temperature of air was kept at 30, 50, or 70°C., thereby altering the flow rate of air, and the volume of gasevolving from the fuel electrode was measured. The evolution volume ofgas was determined by underwater conversion. The concentration ofhydrogen in the evolved gas was determined by gas chromatography, andthe rate of hydrogen evolution was determined based on the result.

The results are shown in FIG. 3.

Evolution of hydrogen from the fuel electrode of the cell was confirmedwith reduction of the flow rate of air for all the temperatures tested.The rate of hydrogen evolution becomes high as the temperature israised. Studies of relation of the open-circuit voltage (open voltage)with the flow rate of air indicate that as the flow rate of air becomeslow, the open-circuit voltage of the cell tends to decline.

FIG. 4 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 3.

From this, it was found that the rate of hydrogen evolution (volume ofhydrogen evolution) tends to depend on the open-circuit voltage, andthat hydrogen evolves when the open-circuit voltage is in the range of400 to 600 mV. The rate of hydrogen evolution is the highest around 450mV for all the temperatures tested.

Next, fuel was flowed at 8 ml/min and air at 120 ml/min at 70° C. toallow gas to evolve, and the concentration of hydrogen in the gas wasdetermined by gas chromatography.

As a result, it was found that the gas contains hydrogen at about 70%,and carbon dioxide at about 15%. CO was not detected.

Hydrogen Generating Example 1-2

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. The temperature of the cell was kept at 70° C., and 1Maqueous solution of methanol (fuel) was provided at the flow rate of 2,8, or 15 ml/min. Then, relations of the flow rate of fuel, the flow rateof air, the rate of hydrogen evolution and open-circuit voltage with theflow rate of air were shown in FIG. 5.

From the graph it was found that as the flow rate of fuel decreases, therate of hydrogen evolution becomes larger.

FIG. 6 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 5.

From this, it was found that the rate of hydrogen evolution depends onthe open-circuit voltage, and is the highest around 450 mV for all thefuel flows tested as in hydrogen generating example 1-1.

In this generating example, the highest rate of hydrogen evolution 14.48ml/min was obtained at the open-circuit voltage of 442 mV (operationtemperature: 70° C.; concentration of fuel: 1M; flow rate of fuel: 2ml/min; and flow rate of air: 100 ml/min). The concentration of hydrogenin the evolved gas was determined by gas chromatography as in example1-1, and found to be about 70%.

Hydrogen Generating Example 1-3

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. The temperature of the cell was kept at 70° C., andaqueous solution of methanol (fuel) at a fuel concentration of 0.5, 1 or2M was applied at a constant flow rate of 8 ml/min. Then, relations ofthe flow rate of fuel, the flow rate of air, the rate of hydrogenevolution and open-circuit voltage with the flow rate of air were shownin FIG. 7.

From the graph it was found that as the concentration of fuel decreases,the rate of hydrogen evolution becomes larger.

FIG. 8 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 7.

From this, it was found that the rate of hydrogen evolution depends onthe open-circuit voltage, and that hydrogen evolves when theopen-circuit voltage is in the range of 300 to 600 mV. The rate ofhydrogen evolution is the highest around 450 mV for all the fuelconcentrations tested as in hydrogen generating example 1-1.

Hydrogen Generating Example 1-4

Next, effect of the thickness of electrolyte membrane on the evolutionvolume of gas was studied.

The hydrogen generating cell was constructed similarly to the aboveexamples, using a Nafion 112 (Dupont) having a thickness of 50 μm,instead of Nafion 115 (Dupont) having a thickness of 130 μm as used inthe above examples 1-1 to 1-3. The cell was operated: temperature at 70°C.; concentration of fuel at 1M; and flow rate of fuel at 8 ml/min, andrelations of the flow rate of fuel, the flow rate of air and the rate ofhydrogen evolution with the flow rate of air were studied.

Both Nafion 115 and 112 membranes are made of the same material as asingle difference in their thickness. Thus, only the thickness ofelectrolyte membranes serves as a parameter to be studied in theexperiment. The study results are summarized in FIG. 9.

FIG. 10 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 9.

From this, it was found that the rate of hydrogen evolution was similarregardless of the thickness of electrolyte membrane. As seen from thefigure, the rate of hydrogen evolution depends on the open-circuitvoltage, and is the highest around 450 mV.

Hydrogen Generating Example 1-5

A hydrogen generating cell constructed as in hydrogen generating example1-1 was placed in an electric furnace where hot air was circulated. Thetemperature of the cell was kept at 30, 50, 70, or 90° C., air wasflowed at a rate of 0 to 250 ml/min to the air electrode, and 1M aqueoussolution of methanol was flowed at a rate of 5 ml/min to the fuelelectrode. Then, the open-circuit voltage, and the rate of hydrogenevolution from the fuel electrode were monitored and analyzed.

Relation of the rate of hydrogen evolution with the flow rate of air isrepresented in FIG. 11.

Similarly to example 1-1, the evolution of hydrogen from the fuelelectrode was confirmed with reduction of the flow rate of air for allthe temperatures tested. The rate of hydrogen evolution becomes high asthe temperature is raised. Studies of relation of the open-circuitvoltage (open voltage) with the flow rate of air indicate that as theflow rate of air becomes low, the open-circuit voltage of the cell tendsto decline.

FIG. 12 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 11.

From this, it was found that the rate of hydrogen evolution depends onthe open-circuit voltage, and hydrogen evolves when the open-circuitvoltage is in the range of 300 to 700 mV. The rate of hydrogen evolutionis the highest around 470 to 480 mV when the temperature is kept at 30to 70° C., while the peak is shifted to 440 mV when the temperature israised to 90° C.

Hydrogen Generating Example 1-6

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. The temperature of cell was kept at 50° C., and fuel wasapplied at the flow rate of 1.5, 2.5, 5.0, 7.5, or 10.0 ml/min. Then,relations of the flow rate of fuel, the flow rate of air and the rate ofhydrogen evolution, with the flow rate of air were shown in FIG. 13.

From this, it was found that in contrast with example 1-2 where thetemperature was kept at 70° C. as the flow rate of fuel increases, therate of hydrogen evolution becomes larger.

FIG. 14 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 13.

From this, it was found that the rate of hydrogen evolution depends onthe open-circuit voltage, and hydrogen evolves when the open-circuitvoltage is in the range of 300 to 700 mV. The rate of hydrogen evolutionis the highest around 450 to 500 mV.

After determining the consumption of methanol in fuel and the rate ofhydrogen evolution when the flow rate of fuel is varied, the energyefficiency under open-circuit condition was determined by calculation inaccordance with the equation described below (which is different fromthe equation used for determining the energy efficiency of a chargingcondition). As a result it was found that, under open-circuit condition,the energy efficiency was 17% when fuel flows at 5.0 ml/min, and 22%when fuel flows at 2.5 ml/min.Efficiency (%) of a hydrogen generating system under open-circuitcondition=(change of the standardized enthalpy of hydrogenevolved/change of enthalpy of methanol consumed)×100

Hydrogen Generating Example 1-7

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. The temperature of cell was kept at 50° C., and aqueoussolution of methanol (fuel) was applied at a constant flow rate of 5ml/min while the concentration of fuel was varied to 0.5, 1, 2, 3M.Then, relations of the flow rate of air and the rate of hydrogenevolution with the flow rate of air were shown in FIG. 15.

From this, it was found that as the concentration of fuel decreases, thepeak of the rate of hydrogen evolution is observed with reduction of theflow rate of air.

FIG. 16 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 15.

From this, it was found that the rate of hydrogen evolution depends onthe open-circuit voltage, and hydrogen evolves when the open-circuitvoltage is in the range of 300 to 700 mV. The rate of hydrogen evolutionis the highest around 470 mV for all the concentrations of fuel tested.

Hydrogen Generating Example 1-8

The same hydrogen generating cell as that of hydrogen generating example1-1 was used (except that the air electrode consisted of an oxidizingelectrode to which oxidizing gas was flowed). The cell was operated:temperature at 50° C.; concentration of fuel at 1M; and flow rate offuel at 5 ml/min, while the concentration of oxygen being varied to 10,21, 40, or 100% and relations of the open-circuit voltage and the rateof hydrogen evolution with the flow rate of oxidizing gas were studied.The results are shown in FIG. 17. The oxidizing gas containing 21%oxygen was represented by air, and the oxidizing gas containing 10%oxygen was obtained by mixing air with nitrogen. The oxidizing gascontaining 40% oxygen was obtained by adding oxygen (100% oxygen) toair.

From this, it was found that as the concentration of oxygen increases,the flow rate of oxidizing gas becomes smaller.

FIG. 18 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 17.

From this, it was found that the rate of hydrogen evolution depends onthe open-circuit voltage, and hydrogen evolves when the open-circuitvoltage is in the range of 400 to 800 mV. The rate of hydrogen evolutionis the highest at 490 to 530 mV.

Hydrogen Generating Example 1-9

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. The cell was operated at 50° C. with the flow of air tothe air electrode kept at 60 ml/min and the flow of aqueous solution ofmethanol (fuel) to the fuel electrode kept at 2.6 ml/min to cause gas toevolve. A 200 cc of sample was collected from the gas, and theconcentration of CO of the gas was determined by gas chromatography. NoCO was detected in the gas (1 ppm or lower). Under the measurementcondition the open-circuit voltage of the cell was 477 mV and the rateof hydrogen evolution was 10 ml/min.

Hydrogen Generating Example 1-10

The same hydrogen generating cell with that of Example 1-1 was used(except that the air electrode consisted of an oxidizing electrode towhich liquid hydrogen peroxide was flowed). The cell was placed in anelectric furnace where hot air was circulated. The cell was operatedwhile the temperature being kept at 30, 50, 70, or 90° C. with the flowof 1M H₂O₂ (hydrogen peroxide) to the oxidizing electrode kept at 1-8ml/min and the flow of 1M aqueous solution of methanol (fuel) to thefuel electrode kept at 5 ml/min. Relations of the open-circuit voltageand the rate of hydrogen evolution with the flow rate of hydrogenperoxide were studied.

Relation of the rate of hydrogen evolution with the flow rate of H₂O₂ isrepresented in FIG. 19.

Similarly to hydrogen generating example 1-1, the evolution of hydrogenfrom the fuel electrode of the cell was confirmed with reduction of theflow rate of H₂O₂ for all the temperatures tested. The rate of hydrogenevolution becomes high as the temperature is raised. Studies of relationof the open-circuit voltage with the flow rate of H₂O₂ indicate that asthe flow rate of H₂O₂ becomes low, the open-circuit voltage of the celltends to decline.

FIG. 20 shows a graph for indicating relationship between theopen-circuit voltage and the rate of hydrogen evolution, both adaptedfrom the results of FIG. 19.

From this, it was found that the rate of hydrogen evolution depends onthe open-circuit voltage, and hydrogen evolves when the open-circuitvoltage is in the range of 300 to 600 mV. The rate of hydrogen evolutionis the highest around 500 mV when the temperature is kept at 30 to 50°C., while the peak is shifted to 450 mV when the temperature is raisedto 70 to 90° C.

What is important here is that no current or voltage was provided fromoutside to the hydrogen generating cells of Example 1. The cell was onlyconnected to an electrometer for monitoring the open-circuit voltagewhich has an internal impedance of 1 GΩ or higher, while the cell wassupplied with fuel and oxidizing agent.

In other words, the hydrogen generating cell of Example 1 converted partof fuel into hydrogen receiving no external energy except for fuel andoxidizing agent.

In addition, conversion of fuel into hydrogen occurred at a surprisinglylow temperature of 30 to 90° C. In view of these facts, the hydrogengenerating device of the invention is likely to be novel and the effectto use this hydrogen generating device in the hydrogen supply system isprofound.

EXAMPLE 2

Illustrative examples of the hydrogen generating device used in thehydrogen supply system as defined by claim 4 of the invention(discharging condition) will be presented below.

Hydrogen Generating Example 2-1

The structure of hydrogen generating cells described in Example 2(illustrative examples 2-1 to 2-8) with means for withdrawing electricenergy is outlined in FIG. 21.

The hydrogen generating cells of Example 2 are the same in structure asthose of hydrogen generating example 1-1 except that the cell comprisesa fuel electrode as a negative electrode and an air electrode as apositive electrode with means for withdrawing electric energy.

The hydrogen generating cell was placed in an electric furnace where hotair was circulated. The cell was operated while the temperature(operation temperature) being kept at 50° C. with the flow rate of airto the air electrode kept at 10 to 100 ml/min and the flow of 1M aqueoussolution of methanol (fuel) to the fuel electrode kept at 5 ml/min tocause gas to evolve. Then, while the external current flowing betweenthe air electrode and the fuel electrode being varied, the operationvoltage between the fuel electrode and the air electrode, the volume ofgas evolved from the fuel electrode and gas composition were monitoredand analyzed. The concentration of hydrogen in the generated gas wasdetermined by gas chromatography.

Relation of the operation voltage with the current density withdrawnrevealed in the test is shown in FIG. 22.

It was found that as the flow rate of air is reduced, the dischargeablelimit current density becomes smaller with the reduction of theoperation voltage.

FIG. 23 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 22.

From this, it was found that the rate of hydrogen evolution (volume ofhydrogen evolution) depends on the operation voltage, and gas evolveswhen the operation voltage is in the range of 300 to 600 mV. Moreover,when the flow rate of air is in the range of 50 to 60 ml/min, hydrogenevolves most readily: when the flow rate of air is excessively large as100 ml/min, no evolution of hydrogen is detected.

Next, the cell was operated: temperature at 50° C.; flow rate of fuel at5 ml/min; flow rate of air at 60 ml/min; and current density at 8.4mA/cm² to cause gas to evolve. The concentration of hydrogen in the gaswas determined by gas chromatography.

As a result, it was found that the gas contained hydrogen at about 74%,and hydrogen evolved at a rate of 5.1 ml/min. No CO was detected.

Hydrogen Generating Example 2-2

The same hydrogen generating cell as that of hydrogen generating example2-1 was used. The cell was operated while the temperature being kept at30° C. with the flow rate of air to the air electrode kept at 30-100ml/min and the flow of 1M aqueous solution of methanol (fuel) to thefuel electrode kept at 5 ml/min. Then, while the current flowing betweenthe air electrode and the fuel electrode being varied, the operationvoltage between the fuel electrode and the air electrode, and the rateof hydrogen evolution occurring from the fuel electrode were monitoredand analyzed.

Relation of the operation voltage with the current density withdrawnrevealed in the test is shown in FIG. 24.

It was found that as the flow rate of air is reduced, the dischargeablelimit current density becomes smaller with the reduction of operationvoltage.

FIG. 25 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 24.

From this, it was found that the rate of hydrogen evolution depends onthe operation voltage, and hydrogen evolves when the operation voltageis in the range of 200 to 540 mV. Hydrogen evolves when the flow rate ofair is in the range of 30 to 70 ml/min. When the flow rate of air is 100ml/min, scarcely any evolution of hydrogen is detected.

Hydrogen Generating Example 2-3

The same hydrogen generating cell as that of hydrogen generating example2-1 was used. The cell was operated while the temperature being kept at70° C. with the flow rate of air to the air electrode kept at 50-200ml/min and the flow of 1M aqueous solution of methanol (fuel) to thefuel electrode kept at 5 ml/min. Then, while the current flowing betweenthe air electrode and the fuel electrode being varied, the operationvoltage between the fuel electrode and the air electrode, and the rateof hydrogen evolution occurring from the fuel electrode were monitoredand analyzed.

Relation of the operation voltage with the current density withdrawnrevealed in the test is shown in FIG. 26.

It was found that as the flow rate of air is reduced, the dischargeablelimit current density becomes smaller with the reduction of theoperation voltage.

FIG. 27 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 26.

From this, it was found that the rate of hydrogen evolution depends onthe operation voltage, and hydrogen evolves when the operation voltageis in the range of 200 to 500 mV. Hydrogen is ready to evolve when theflow rate of air is in the range of 50 to 100 ml/min. When the flow rateof air is excessively large as 150 to 200 ml/min, scarcely any evolutionof hydrogen is detected.

Hydrogen Generating Example 2-4

The same hydrogen generating cell as that of hydrogen generating example2-1 was used. The cell was operated while the temperature being kept at90° C. with the flow of air to the air electrode kept at 50-250 ml/minand the flow of 1M aqueous solution of methanol (fuel) to the fuelelectrode kept at 5 ml/min. Then, while the current flowing between theair electrode and the fuel electrode being varied, the operation voltagebetween the fuel electrode and the air electrode, and the rate ofhydrogen evolution occurring from the fuel electrode were monitored andanalyzed.

Relation of the operation voltage with the current density withdrawnrevealed in the test is shown in FIG. 28.

It was found that as the flow rate of air is reduced, the dischargeablelimit current density becomes smaller with the reduction of theoperation voltage.

FIG. 29 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 28.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and hydrogen evolves when the operationvoltage is in the range of 200 to 500 mV. Hydrogen is ready to evolvewhen the flow rate of air is in the range of 50 to 100 ml/min. When theflow rate of air is at 250 ml/min, scarcely any evolution of hydrogen isdetected.

Next, when the cell is operated with the flow of air being kept at 50ml/min while respective temperatures are varied as in hydrogengenerating examples 2-1 to 2-4, FIG. 30 shows relation of the currentdensity withdrawn with the operation voltage while FIG. 31 showsrelation of the rate of hydrogen evolution with the operation voltage.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and as the temperature becomes higher,hydrogen evolves at a lower operation voltage and the evolution volumebecomes larger.

Further, when the cell is operated with the flow of air being kept at100 ml/min while respective temperatures are varied as in hydrogengenerating examples 2-1 to 2-4, FIG. 32 shows relation of the currentdensity withdrawn with the operation voltage while FIG. 33 showsrelation of the rate of hydrogen evolution with the operation voltage.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and as the temperature becomes higher,hydrogen evolves at a lower operation voltage and the evolution volumebecomes larger. It was also found that when the flow rate of air isexcessively large as 100 ml/min, scarcely any evolution of hydrogen isdetected when the temperature is kept as low as 30 or 50° C.

Hydrogen Generating Example 2-5

The same hydrogen generating cell as that of hydrogen generating example2-1 was used. The cell was operated while the temperature being kept at50° C. with the flow of air to the air electrode kept at 50 ml/min andthe flow rate of fuel to the fuel electrode varied to 1.5, 2.5, 5.0,7.5, or 10.0 ml/min. Then, while the current flowing between the airelectrode and the fuel electrode being varied, the operation voltagebetween the fuel electrode and the air electrode, and the rate ofhydrogen evolution occurring from the fuel electrode were monitored andanalyzed.

Relation of the operation voltage with the current density withdrawnrevealed in the test is shown in FIG. 34.

It was found that the dischargeable limit current density hardly changeseven when the flow of fuel is varied.

FIG. 35 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 34.

From this, it was found that the rate of hydrogen evolution depends onthe operation voltage, and hydrogen evolves when the operation voltageis in the range of 300 to 500 mV. The rate of hydrogen evolution is highwhen the operation voltage is in the range of 450 to 500 ml/min.

It was found that the rate of hydrogen evolution is hardly affected bythe flow rate of fuel.

Hydrogen Generating Example 2-6

The same hydrogen generating cell as that of hydrogen generating example2-1 was used. The cell was operated while the temperature being kept at50° C. with the flow of air to the air electrode kept at 50 ml/min andthe constant flow of fuel to the fuel electrode kept at 5 ml/min whilefuel concentration being varied to 0.5, 1, 2, or 3M. Then, while thecurrent flowing between the air electrode and the fuel electrode beingvaried, the operation voltage between the fuel electrode and the airelectrode, and the rate of hydrogen evolution occurring from the fuelelectrode were monitored and analyzed.

Relation of the voltage with the current density withdrawn revealed inthe test is shown in FIG. 36.

It was found that the dischargeable limit current density declines asthe concentration of fuel becomes higher with the reduction of operationvoltage.

FIG. 37 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 36.

From this, it was found that the rate of hydrogen evolution depends onthe voltage, and hydrogen evolves when the operation voltage is in therange of 300 to 600 mV.

Hydrogen evolves most vigorously when the concentration of fuel is 1M.

Hydrogen Generating Example 2-7

The same hydrogen generating cell as that of hydrogen generating example2-1 was used (except that the air electrode consisted of an oxidizingelectrode to which oxygen was flowed). The cell was operated while thetemperature being kept at 50° C. with the flow of oxidizing gas to theoxidizing electrode kept at 14.0 ml/min and the constant flow of 1M fuelconcentration to the fuel electrode kept at 5 ml/min, while theconcentration of oxygen being varied to 10, 21, 40, or 100%. Then, whilethe current flowing between the oxidizing electrode and the fuelelectrode being varied, the operation voltage between the fuel electrodeand the oxidizing electrode, and the rate of hydrogen evolutionoccurring from the fuel electrode were monitored and analyzed. Theoxidizing gas containing 21% oxygen was represented by air, and theoxidizing gas containing 10% oxygen was obtained by mixing air withnitrogen. The oxidizing gas containing 40% oxygen was obtained by addingoxygen (100% oxygen concentration) to air.

Relation of the operation voltage with the current density withdrawnrevealed in the test is shown in FIG. 38.

It was found that the operation voltage declines as the concentration ofoxygen becomes smaller with the reduction of dischargeable limit currentdensity.

FIG. 39 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 38.

From this, it was found that the rate of hydrogen evolution depends onthe operation voltage, and hydrogen evolves when the operation voltageis in the range of 300 to 600 mV.

The rate of hydrogen evolution tends to be high as the concentration ofoxygen becomes higher.

Hydrogen Generating Example 2-8

The same hydrogen generating cell as that of hydrogen generating example2-1 was used (except that the air electrode consisted of an oxidizingelectrode to which liquid hydrogen peroxide was flowed). The hydrogengenerating cell was placed in an electric furnace where hot air wascirculated. The cell was operated while the temperature being varied to30, 50, 70, or 90° C. with the flow of 1M aqueous solution of H₂O₂(hydrogen peroxide) to the oxidizing electrode varied from 2.6 to 5.5ml/min, and the flow of 1M aqueous solution of methanol (fuel) to thefuel electrode kept at 5 ml/min. Then, while the current flowing betweenthe oxidizing electrode and the fuel electrode being varied, theoperation voltage between the fuel electrode and the oxidizingelectrode, and the rate of hydrogen evolution occurring from the fuelelectrode were monitored and analyzed. The flow rate of hydrogenperoxide was adjusted such that the open-circuit voltage wasapproximately equal to 500 mV for all the temperatures tested.

Relation of the operation voltage with the current density withdrawnrevealed in the test is shown in FIG. 40.

It was found that the decline of operation voltage with the increase ofcurrent density takes a similar course when the temperature is kept at70 to 90° C., while operation voltage undergoes a sharp fall when thetemperature is decreased to 30° C. with the reduction of dischargeablelimit current density.

FIG. 41 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 40.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and hydrogen evolves when the operationvoltage is in the range of 300 to 500 mV. Hydrogen is most ready toevolve when the temperature is 90° C. Hydrogen does not evolve unlessthe operation voltage is raised sufficiently high, when the temperatureis at the low level tested.

What is important here is that current was withdrawn outside from thehydrogen generating cells of Example 2. In other words, the hydrogengenerating cell of Example 2 converted part of fuel into hydrogen whilewithdrawing electric energy to outside. In addition, conversion of fuelinto hydrogen occurred at a surprisingly low temperature of 30 to 90° C.In view of these facts, the hydrogen generating device of the inventionis likely to be novel and the effect to use this hydrogen generatingdevice in the hydrogen supply system is profound.

EXAMPLE 3

Illustrative examples of the hydrogen generating device used in thehydrogen supply system as defined by claim 5 of the invention (chargingcondition) will be presented below.

Hydrogen Generating Example 3-1

The structure of hydrogen generating cells described in Example 3(hydrogen generating examples 3-1 to 3-8) with means for providingelectric energy from outside is outlined in FIG. 42.

The hydrogen generating cells are the same in structure as those ofhydrogen generating example 1-1 except that the cell comprises a fuelelectrode as cathode and an oxidizing electrode as anode with means forproviding electric energy from outside.

The hydrogen generating cell was placed in an electric furnace where hotair was circulated. The cell was operated while the temperature(operation temperature) being kept at 50° C. with the flow of air to theair electrode kept at 10 to 80 ml/min and the flow of 1M aqueoussolution of methanol (fuel) to the fuel electrode kept at 5 ml/min.Then, while the current flowing between the air electrode and the fuelelectrode being varied by means of a DC power source from outside, theoperation voltage between the fuel electrode and the air electrode, thevolume of gas evolved from the fuel electrode and gas composition weremonitored and analyzed. The energy efficiency of charging condition wasdefined as a ratio of the chemical-energy of hydrogen evolved to theelectric energy supplied from outside. The concentration of hydrogen inthe generated gas was determined by gas chromatography, and rate ofhydrogen evolution also determined.

The energy efficiency of a charging condition was calculated based onthe following equation:Energy efficiency (%)=(combustion heat of H₂/electric energyprovided)×100Combustion heat (kJ) of H₂ per minute=(rate of H₂ evolutionml/min/24.47/1000)×286 kJ/mol [HHV]Electric energy (kJ) per minute=(voltage mV/1000×current A×60sec)Wsec/1000

To avoid undue misunderstanding, a few comments are added here. Theobject of this invention lies in obtaining hydrogen gas having a higherenergy content than the electric energy supplied from outside, and theinvention does not aim to gain more energy than the sum of paid energywithout taking any heed to the law of conservation of energy taught bythermodynamics. When the energy balance of the entire system is takeninto view, since part of organic compound-based fuel is oxidized, theenergy expenditure includes, in addition to the electric energy suppliedfrom outside, the chemical energy consumed for the oxidization of thefuel, which will amount to a value equal to or less than 100%. Todistinguish more clearly the inventive method from conventional methodsfor obtaining hydrogen via the electrolysis of water, the energyefficiency of a system defined by the ratio of the chemical energy ofevolved hydrogen to the electric energy supplied from outside will beused here.

Relation of the rate of hydrogen evolution with the current densityapplied in the test is shown in FIG. 43.

It was found that the efficiency of hydrogen evolution (efficiency ofhydrogen evolution relative to electric energy supplied) becomes equalto or more than 100% (100% efficiency of hydrogen evolution isrepresented by the dashed line in FIG. 43) in certain areas when thecurrent density is kept not more than 40 mA/cm². This suggests that itis possible to obtain hydrogen whose energy content is larger than theelectric energy supplied from outside by operating the cell in thoseareas.

FIG. 44 shows a graph for indicating relationship between the rate ofhydrogen evolution and the operation voltage, both adapted from theresults of FIG. 43.

From this, it was found that the rate of hydrogen evolution (volume ofhydrogen evolution) tends to depend on the operation voltage, andhydrogen evolves when the operation voltage is equal to or larger than400 mV, and the rate of hydrogen evolution becomes virtually constantwhen the operation voltage becomes equal to or larger than 600 mV, andthe rate of hydrogen evolution becomes larger (hydrogen is readier toevolve) with reduction of the flow rate of air.

Relation of the operation voltage with the current density applied isshown in FIG. 45.

The areas in FIG. 43 where the efficiency of hydrogen evolution is 100%or more fall below the line defined by the operation voltage being equalto or lower than 600 mV in FIG. 45.

Relation of the energy efficiency with the operation voltage is shown inFIG. 46.

From this, it was found that the energy efficiency is equal to or largerthan 100% even when the operation voltage is around 1000 mV, and theenergy efficiency is particularly high when the operation voltage iskept equal to or smaller than 600 mV, and the flow of air is kept at 30to 50 ml/min.

Next, the cell was operated under a condition of high energy efficiency(1050%): temperature at 50° C.; flow rate of fuel at 5 ml/min; flow rateof air at 50 ml/min; and current density at 4.8 mA/cm² to cause gas toevolve. The concentration of hydrogen in the gas was determined by gaschromatography. As a result it was found that the gas contained hydrogenat about 86%, and hydrogen evolved at a rate of 7.8 ml/min. No CO wasdetected.

Hydrogen Generating Example 3-2

The same hydrogen generating cell as that of hydrogen generating example3-1 was used. The cell was operated while the temperature being kept at30° C. with the flow of air to the air electrode varied from 10 to 70ml/min and the flow of 1M aqueous solution of methanol (fuel) to thefuel electrode kept at 5 ml/min. Then, while the current flowing betweenthe air electrode and the fuel electrode being varied by means of a DCpower source from outside, the operation voltage between the fuelelectrode and the air electrode, the rate of hydrogen evolutionoccurring from the fuel electrode, and the energy efficiency weremonitored and analyzed.

In this test, relation of the rate of hydrogen evolution with thecurrent density applied is shown in FIG. 47, and relation of the rate ofhydrogen evolution with the operation voltage is shown in FIG. 48.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and hydrogen evolves when the operationvoltage is equal to or larger than 400 mV; hydrogen is readier to evolvewith reduction of the flow rate of air; and the rate of hydrogenevolution becomes virtually constant with the air flow of 10 ml/min,when the operation voltage becomes equal to or larger than 600 mV, whilethe rate of hydrogen evolution tends to grow with the air flow of 30ml/min, when the operation voltage becomes equal to or larger than 800mV, and thus no hydrogen will evolve when air flows at a higher rateunless the operation voltage is raised sufficiently high.

Relation of the energy efficiency with the operation voltage is shown inFIG. 49.

From this, it was found that the energy efficiency is equal to or largerthan 100% even when the operation voltage is around 1000 mV, and theenergy efficiency is particularly high with the air flow of 30 ml/minwhen the operation voltage is kept equal to or smaller than 600 mV.

Hydrogen Generating Example 3-3

The test was performed under the same condition as in hydrogengenerating example 3-2 except that the temperature of the cell was keptat 70° C. The operation voltage between the fuel electrode and the airelectrode, and rate of hydrogen evolution on the fuel electrode andenergy efficiency were monitored and analyzed.

Relation of the rate of hydrogen evolution with the current densityapplied during the test is shown in FIG. 50, and relation of the rate ofhydrogen evolution with the operation voltage is shown in FIG. 51.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and hydrogen evolves when the operationvoltage is equal to or larger than 400 mV; hydrogen is readier to evolvewith reduction of the flow rate of air; and the rate of hydrogenevolution becomes virtually constant with the air flow of 10 ml/min,when the operation voltage becomes equal to or larger than 600 mV, whilethe rate of hydrogen evolution tends to grow with the air flow of 30ml/min, when the operation voltage becomes equal to or larger than 800mV, and thus no hydrogen will evolve when air flows at a higher rateunless the operation voltage is raised sufficiently high.

Relation of the energy efficiency with the operation voltage is shown inFIG. 52.

It was found that the energy efficiency is equal to or larger than 100%even when the operation voltage is around 1000 mV, and the energyefficiency is particularly high with the flow rate of air of 10 to 30ml/min when the operation voltage is kept equal to or smaller than 600mV.

Hydrogen Generating Example 3-4

The same hydrogen generating cell as that of hydrogen generating example3-1 was used. The cell was operated while the temperature being kept at90° C. with the flow rate of air to the air electrode varied from 10 to200 ml/min and the flow of 1M aqueous solution of methanol (fuel) to thefuel electrode kept at 5 ml/min. Then, while the current flowing betweenthe air electrode and the fuel electrode being varied by means of a DCpower source from outside, the operation voltage between the fuelelectrode and the air electrode, the rate of hydrogen evolutionoccurring from the fuel electrode, and the energy efficiency weremonitored and analyzed.

Relation of the rate of hydrogen evolution with the current densityapplied is shown in FIG. 53, and relation of the rate of hydrogenevolution with the operation voltage is shown in FIG. 54.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and hydrogen evolves when the operationvoltage is equal to or larger than 300 mV; hydrogen is readier to evolvewith reduction of the flow rate of air; and the rate of hydrogenevolution becomes virtually constant with the air flow of 10 ml/min,when the operation voltage becomes equal to or larger than 500 mV, whilethe rate of hydrogen evolution tends to grow with the air flow of 50 to100 ml/min, when the operation voltage becomes equal to or larger than800 mV, and thus no hydrogen will evolve when air flows at 200 ml/minunless the operation voltage is raised higher than 800 mV.

Relation of the energy efficiency with the operation voltage is shown inFIG. 55.

From this, it was found that the energy efficiency is equal to or largerthan 100% even when the operation voltage is around 1000 mV, and theenergy efficiency is particularly high with the flow of air of 50 ml/minwhen the operation voltage is kept equal to or smaller than 500 mV.

Next, for hydrogen generating examples 3-1 to 3-4 where operationtemperature was varied with the flow of air kept at 50 ml/min, relationof the rate of hydrogen evolution with the current density applied isshown in FIG. 56, while relation of the rate of hydrogen evolution withthe operation voltage is shown in FIG. 57.

From this, it was found that the rate of hydrogen evolution tends todepend on the temperature: hydrogen evolves at a low operation voltageand the rate of hydrogen evolution becomes higher as the temperature israised.

Relation of the energy efficiency with the operation voltage is shown inFIG. 58.

It was found that the energy efficiency is equal to or larger than 100%even when the operation voltage is around 1000 mV, and the energyefficiency is particularly high when the operation voltage is kept equalto or smaller than 600 mV.

Hydrogen Generating Example 3-5

The same hydrogen generating cell with that of hydrogen generatingexample 3-1 was used. The cell was operated while the temperature beingkept at 50° C. with the flow of air to the air electrode kept at 50ml/min and the flow of fuel to the fuel electrode varied to 1.5, 2.5,5.0, 7.5, or 10.0 ml/min. Then, while the current flowing between theair electrode and the fuel electrode being varied by means of a DC powersource from outside, the operation voltage between the fuel electrodeand the air electrode, the rate of hydrogen evolution occurring from thefuel electrode, and the energy efficiency were monitored and analyzed.

Relation of the rate of hydrogen evolution with the current densityapplied is shown in FIG. 59, and relation of the rate of hydrogenevolution with the operation voltage is shown in FIG. 60.

It was found that the rate of hydrogen evolution tends to depend on theoperation voltage, and hydrogen evolves when the operation voltage isequal to or larger than 400 mV; hydrogen is readier to evolve withincrease of the flow rate of fuel; and the rate of hydrogen evolutiontends to grow when the operation voltage is equal to or larger than 800mV for all the flow rates of fuel tested.

Relation of the energy efficiency with the operation voltage is shown inFIG. 61.

It was found that the energy efficiency is equal to or larger than 100%even when the operation voltage is around 1000 mV, and the energyefficiency is particularly high when the operation voltage is kept equalto or smaller than 600 mV.

Hydrogen Generating Example 3-6

The same hydrogen generating cell as that of hydrogen generating example3-1 was used. The cell was operated while the temperature being kept at50° C. with the flow of air to the air electrode kept at 50 ml/min andthe constant flow of fuel to the fuel electrode kept at 5 ml/min whilefuel concentration being varied to 0.5, 1, 2, or 3M. Then, while theexternal current flowing between the air electrode and the fuelelectrode being varied by means of a DC power source from outside, theoperation voltage between the fuel electrode and the air electrode, therate of hydrogen evolution occurring from the fuel electrode, and theenergy efficiency were monitored and analyzed.

Relation of the rate of hydrogen evolution with the current densityapplied is shown in FIG. 62, and relation of the rate of hydrogenevolution with the operation voltage is shown in FIG. 63.

From this, it was found that the rate of hydrogen evolution grows almostlinearly with the increase of current density provided that the currentdensity is equal to or higher than 0.02 A/cm².

It was also found that the rate of hydrogen evolution tends to depend onthe operation voltage, and hydrogen evolves when the operation voltageis equal to or larger than 400 mV; hydrogen is readier to evolve withincrease of the concentration of fuel, and the rate of hydrogenevolution grows sharply under the fuel concentration of 2M or 3M, whenthe operation voltage approaches 400 to 500 mV; and the rate of hydrogenevolution becomes virtually constant under the fuel concentration of 1Mwhen the operation voltage is in the range of 400 to 800 mV, while therate of hydrogen evolution tends to grow when the operation voltagebecomes equal to or larger than 800 mV, and no hydrogen will evolve whenthe fuel concentration is lower than this level (1M) unless theoperation voltage is raised sufficiently high.

Relation of the energy efficiency with the operation voltage is shown inFIG. 64.

It was found that the energy efficiency is equal to or larger than 100%even when the operation voltage is around 1000 mV except for a casewhere the fuel concentration is kept at 0.5M, and the energy efficiencyis particularly high with the concentration of the fuel being 1, 2 or 3Mwhen the operation voltage is kept equal to or smaller than 600 mV. Whenthe concentration of fuel was 0.5M, no hydrogen evolved when theoperation voltage was low. Under this condition, the cell behaved quitedifferently in terms of energy efficiency.

Hydrogen Generating Example 3-7

The same hydrogen generating cell with that of hydrogen generatingexample 3-1 was used (except that the air electrode consisted of anoxidizing electrode to which oxidizing gas was flowed). The cell wasoperated while the temperature being kept at 50° C. with the constantflow of 1M fuel to the fuel electrode kept at 5 ml/min and the flow ofoxidizing gas to the oxidizing electrode kept at 14.0 ml/min whileoxygen concentration being varied to 10, 21, 40, or 100%. Then, whilethe current flowing between the oxidizing electrode and the fuelelectrode being varied by means of a DC power source from outside, theoperation voltage between the fuel electrode and the oxidizingelectrode, the rate of hydrogen evolution occurring from the fuelelectrode, and the energy efficiency were monitored and analyzed. Theoxidizing gas containing 21% oxygen was represented by air, and theoxidizing gas containing 10% oxygen was obtained by mixing air withnitrogen. The oxidizing gas containing 40% oxygen was obtained by addingoxygen (100% oxygen) to air.

Relation of the rate of hydrogen evolution with the current densityapplied is shown in FIG. 65, and relation of the rate of hydrogenevolution with the operation voltage is shown in FIG. 66.

From this, it was found that the rate of hydrogen evolution grows almostlinearly with the increase of current density provided that the currentdensity is equal to or higher than 0.03 A/cm².

It was also found that the rate of hydrogen evolution tends to depend onthe operation voltage, and hydrogen evolves when the operation voltageis equal to or larger than 400 mV; hydrogen is readier to evolve withincrease of the concentration of oxygen; and the rate of hydrogenevolution becomes virtually constant under when the operation voltage isin the range of 400 to 800 mV, while it tends to grow when the operationvoltage becomes equal to or larger than 800 mV.

Relation of the energy efficiency with the operation voltage is shown inFIG. 67.

It was found that the energy efficiency is equal to or larger than 100%even when the applied voltage is around 1000 mV, and the energyefficiency is particularly high with the concentration of oxygen beinghigh when the applied voltage is kept equal to or smaller than 600 mV.

Hydrogen Generating Example 3-8

The same hydrogen generating cell as that of hydrogen generating example3-1 was used (except that the air electrode consisted of an oxidizingelectrode to which liquid hydrogen peroxide was flowed). The hydrogengenerating cell was placed in an electric furnace where hot air wascirculated. The cell was operated while the temperature being varied to30, 50, 70, or 90° C. with the flow of 1M aqueous solution of methanolto the fuel electrode kept at 5 ml/min and the flow of 1M H₂O₂ (hydrogenperoxide) to the oxidizing electrode varied from 2.6 to 5.5 ml/min.Then, while the current flowing between the oxidizing electrode and thefuel electrode being varied by means of a DC power source from outside,the operation voltage between the fuel electrode and the oxidizingelectrode, the rate of hydrogen evolution occurring from the fuelelectrode, and the energy efficiency were monitored and analyzed.

The flow rate of hydrogen peroxide was adjusted such that theopen-circuit voltage was approximately equal to 500 mV for all thetemperatures tested.

Relation of the rate of hydrogen evolution with the current densityapplied is shown in FIG. 68, and relation of the rate of hydrogenevolution with the operation voltage is shown in FIG. 69.

From this, it was found that the rate of hydrogen evolution tends todepend on the operation voltage, and hydrogen evolves when the operationvoltage is equal to or larger than 500 mV, and tends to grow when theoperation voltage is equal to or larger than 800 mV; and hydrogen isreadier to evolve with increase of the operation temperature.

Relation of the energy efficiency with the operation voltage is shown inFIG. 70.

It was found that the energy efficiency is equal to or larger than 100%even when the operation voltage is around 1000 mV, and the energyefficiency is particularly high with the temperature of 90° C. when theoperation voltage is kept equal to or smaller than 800 mV.

What is important here is that hydrogen was withdrawn from the hydrogengenerating cells of Example 3 whose energy content exceeded the electriccurrent supplied from outside. In other words, the hydrogen generatingcell of Example 3 generates hydrogen of energy more than inputtedelectric energy. In addition, conversion of fuel into hydrogen occurredat a surprisingly low temperature of 30 to 90° C. In view of thesefacts, the hydrogen generating device of the invention is likely to benovel and the effect to use this hydrogen generating device in thehydrogen supply system is profound.

In the following embodiments, examples to produce hydrogen by thehydrogen generating device used in the hydrogen supply system of theinvention using a fuel other than methanol will be described.

EXAMPLE 4

Hydrogen was generated by the hydrogen generating device used in thehydrogen supply system of the invention as described in claim 3 of theinvention (open circuit condition) using ethanol as a fuel.

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. At the cell temperature of 80° C., the flow of 1M aqueoussolution of ethanol was made at 5 ml/min to flow to the fuel electrodeand the flow of air was made at 65 ml/min to the air electrode. Then,the open-circuit voltage of the cell and the rate of gas evolutiongenerated from the fuel electrode were measured. The hydrogenconcentration in the generated gas was analyzed by a gas chromatographyand the hydrogen evolution rate was acquired.

The result is shown in Table 1:

TABLE 1 Open- Gas H₂ circuit evolution H₂ evolution Air/ voltage/ rate/concentration/ rate/ ml/min mV ml/min % ml/min 65 478 0.6 65.2 0.39

As shown in Table 1, it was confirmed that hydrogen was generated at theopen-circuit voltage of 478 mV, but the hydrogen evolution rate wassmall.

EXAMPLE 5

Hydrogen was generated by the hydrogen generating device used in thehydrogen supply system of the invention as described in claim 3 of theinvention (open circuit condition) using ethylene glycol as a fuel.

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. At the cell temperature of 80° C., the flow of 1M aqueoussolution of ethylene glycol was made at 5 ml/min to flow to the fuelelectrode and the flow of air was made at 105 ml/min to the airelectrode. Then, the open-circuit voltage of the cell and the rate ofgas evolution generated from the fuel electrode were measured. Thehydrogen concentration in the generated gas was analyzed by a gaschromatography and the hydrogen evolution rate was acquired.

The result is shown in Table 2:

TABLE 2 Open- Gas H₂ circuit evolution H₂ evolution Air/ voltage/ rate/concentration/ rate/ ml/min mV ml/min % ml/min 105 474 2.4 88.4 2.12

As shown in Table 2, it was confirmed that hydrogen was generated at theopen-circuit voltage of 474 mV. The hydrogen evolution rate was largerthan the case of aqueous solution of ethanol as a fuel, but considerablysmaller than the case of aqueous solution of methanol.

EXAMPLE 6

Hydrogen was generated by the hydrogen generating device used in thehydrogen supply system of the invention as described in claim 3 of theinvention (open circuit condition) using 2-propanol as a fuel.

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. At the cell temperature of 80° C., the flow of 1M aqueoussolution of 2-propanol was made at 5 ml/min to flow to the fuelelectrode and the flow of air was made at 35 ml/min to the airelectrode. Then, the open-circuit voltage of the cell and the rate ofgas evolution generated from the fuel electrode were measured. Thehydrogen concentration in the generated gas was analyzed by a gaschromatography and the hydrogen evolution rate was acquired.

The result is shown in Table 3:

TABLE 3 Open- Gas H₂ circuit evolution H₂ evolution Air/ voltage/ rate/concentration/ rate/ ml/min mV ml/min % ml/min 35 514 3.96 95.6 3.78

As shown in Table 3, it was confirmed that hydrogen was generated at theopen-circuit voltage of 514 mV, but the hydrogen evolution rate waslarger than the case of the aqueous solution of ethanol or the aqueoussolution of ethylene glycol as a fuel and the closest to the aqueoussolution of methanol. Particularly, the hydrogen concentration in thegenerated gas was extremely high.

EXAMPLE 7

Hydrogen was generated by the hydrogen generating device used in thehydrogen supply system of the invention as described in claim 3 of theinvention (open circuit condition) using diethyl ether as a fuel.

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. At the cell temperature of 80° C., the flow of 1M aqueoussolution of diethyl ether was made at 5 ml/min to flow to the fuelelectrode and the flow of air was made at 20 ml/min to the airelectrode. Then, the open-circuit voltage of the cell and the rate ofgas evolution generated from the fuel elect-rode were measured. Thehydrogen concentration in the generated gas was analyzed by a gaschromatography and the hydrogen evolution rate was acquired.

The result is shown in Table 4:

TABLE 4 Open- Gas H₂ circuit evolution H₂ evolution Air/ voltage/ rate/concentration/ rate/ ml/min mV ml/min % ml/min 20 565 3.0 7.6 0.23

As shown in Table 4, it was confirmed that hydrogen was generated at theopen-circuit voltage of 565 mV. The hydrogen concentration in thegenerated gas was smaller than the cases using alcohol as a fuel and thehydrogen evolution rate was also small.

EXAMPLE 8

Hydrogen was generated by the hydrogen generating device used in thehydrogen supply system of the invention as described in claim 3 of theinvention (open circuit condition) using formaldehyde, formic acid as afuel.

The same hydrogen generating cell as that of hydrogen generating example1-1 was used. At the cell temperature of 50° C., the flow of 1M aqueoussolution of formaldehyde, the flow of 1M aqueous solution of formic acidwere made at 5 ml/min respectively to flow to the fuel electrode and theflow of air was made at 0 to 100 ml/min to the air electrode. Then, theopen-circuit voltage of the cell and the rate of gas evolution generatedfrom the fuel electrode were measured. The hydrogen concentration in thegenerated gas was analyzed by a gas chromatography and the hydrogenevolution rate was acquired.

The result is shown in FIGS. 71 and 72 with the case where methanol wasused.

As shown in FIG. 71, in the case of formaldehyde, formic acid,generation of hydrogen was confirmed form the fuel electrode of the cellby reducing the air flow rate as in the case of methanol. Also, thehydrogen evolution rate is the largest with methanol, followed byformaldehyde and formic acid. Moreover, it was found out that hydrogenwas not generated unless the air flow rate is reduced in this order.

From FIG. 72, it was found out that in the case of formaldehyde andformic acid, the hydrogen evolution rate (hydrogen evolution volume)also tends to depend on the open-circuit voltage as with methanol andthat hydrogen was generated at the open-circuit voltage of 200 to 800mV. In the case of formic acid, hydrogen was generated in a state wherethe open-circuit voltage was lower than that for methanol, formaldehyde.Also, the peak of hydrogen evolution rate was observed at a lowopen-circuit voltage (about 350 mV) for formic acid, while that ofmethanol, formaldehyde was about 500 mV.

INDUSTRIAL APPLICABILITY

As seen from above, since the hydrogen generating device used in thehydrogen supply system of the invention can generate ahydrogen-containing gas by decomposing a fuel containing an organiccompound at 100° C. or lower, this is useful as a hydrogen supply systemfor supplying hydrogen to a hydrogen storage tank for supplying hydrogento a hydrogen storage container loaded on a fuel cell automobile, a fuelcell automobile. It is also useful as a hydrogen supply system whenhydrogen is used as a treatment gas or the like in manufacturing asemiconductor device.

1. A hydrogen supply system comprising: at least hydrogen supply means for supplying hydrogen to hydrogen storing means and a hydrogen generating device producing hydrogen containing gas to be supplied to the hydrogen supply means, wherein the hydrogen generating device produces the hydrogen containing gas by decomposing a fuel containing an organic compound and comprises a partition membrane, a fuel electrode provided on one surface of the partition membrane for generating hydrogen containing gas, means for supplying a fuel containing the organic compound and water to the fuel electrode, an oxidizing electrode provided on the other surface of the partition membrane, means for supplying an oxidizing agent to the oxidizing electrode, and means for collecting the hydrogen containing gas directly from the fuel electrode, and wherein an operation temperature of the hydrogen generating device is not higher than 100° C.
 2. A hydrogen supply system comprising at least hydrogen supply means for supplying hydrogen to hydrogen storing means and a hydrogen generating device producing hydrogen containing gas to be supplied to the hydrogen supply means, wherein the hydrogen generating device produces the hydrogen containing gas by decomposing a fuel containing an organic compound and comprises a partition membrane, a fuel electrode provided on one surface of the partition membrane, means for supplying a fuel containing the organic compound and water to the fuel electrode, an oxidizing electrode provided on the other surface of the partition membrane, means for supplying an oxidizing agent to the oxidizing electrode, and means for collecting the hydrogen containing gas from the fuel electrode, wherein the hydrogen generating device is an open circuit having neither means for withdrawing electric energy to outside from a hydrogen generating cell constituting the hydrogen generating device, nor means for providing electric energy from outside to the hydrogen generating cell, and wherein an operation temperature of the hydrogen generating device is not higher than 100° C.
 3. The hydrogen supply system as described in claim 1, wherein the hydrogen generating device has means for withdrawing electric energy to outside with the fuel electrode serving as a negative electrode and the oxidizing electrode as a positive electrode.
 4. The hydrogen supply system as described in claim 1, wherein the hydrogen generating device has means for providing electric energy from outside with the fuel electrode serving as cathode and the oxidizing electrode as anode.
 5. The hydrogen supply system as described in claim 1, wherein voltage between the fuel electrode and the oxidizing electrode is 200 to 1000 mV in the hydrogen generating device.
 6. The hydrogen supply system as described in claim 2, wherein voltage between the fuel electrode and the oxidizing electrode is 300 to 800 mV in the hydrogen generating device.
 7. The hydrogen supply system as described in claim 3, wherein voltage between the fuel electrode and the oxidizing electrode is 200 to 600 mV in the hydrogen generating device.
 8. The hydrogen supply system as described in claim 3, wherein voltage between the fuel electrode and the oxidizing electrode and/or the evolution volume of hydrogen-containing gas are/is adjusted by varying the volume of electric energy withdrawn from the hydrogen generating device.
 9. The hydrogen supply system as described in claim 4, wherein voltage between the fuel electrode and the oxidizing electrode is 300 to 1000 mV in the hydrogen generating device.
 10. The hydrogen supply system as described in claim 4, wherein voltage between the fuel electrode and the oxidizing electrode and/or the evolution volume of hydrogen-containing gas are/is adjusted by varying the volume of electric energy provided in the hydrogen generating device.
 11. The hydrogen supply system as described in claim 1, wherein the evolution volume of hydrogen-containing gas is adjusted by varying voltage between the fuel electrode and the oxidizing electrode in the hydrogen generating device.
 12. The hydrogen supply system as described in claim 1, wherein voltage between the fuel electrode and the oxidizing electrode and/or the evolution volume of hydrogen-containing gas are/is adjusted by varying the supply volume of the oxidizing agent in the hydrogen generating device.
 13. The hydrogen supply system as described in claim 1, wherein voltage between the fuel electrode and the oxidizing electrode and/or the evolution volume of hydrogen-containing gas are/is adjusted by varying the concentration of the oxidizing agent in the hydrogen generating device.
 14. The hydrogen supply system as described in claim 1, wherein voltage between the fuel electrode and the oxidizing electrode and/or the evolution volume of hydrogen-containing gas are/is adjusted by varying the supply volume of fuel containing an organic compound and water in the hydrogen generating device.
 15. The hydrogen supply system as described in claim 1, wherein voltage between the fuel electrode and the oxidizing electrode and/or the evolution volume of hydrogen-containing gas are/is adjusted by varying the concentration of fuel containing an organic compound and water in the hydrogen generating device.
 16. The hydrogen supply system as described in claim 1, wherein the organic compound supplied to the fuel electrode of the hydrogen generating device is one or two or more organic compounds selected from a group consisting of alcohol, aldehyde, carboxyl acid and ether.
 17. The hydrogen supply system as described in claim 1, wherein the oxidizing agent supplied to the oxidizing electrode of the hydrogen generating device is an oxygen-containing gas or oxygen.
 18. The hydrogen supply system as described in claim 1, wherein the oxidizing agent supplied to the oxidizing electrode of the hydrogen generating device is a liquid containing hydrogen peroxide solution.
 19. The hydrogen supply system as described in claim 1, wherein the partition membrane of the hydrogen generating device is a proton conducting solid electrolyte membrane. 